mjhjmtu

Yes it is reasonable to leave without finding a replacement. The fact that the company has not properly planned for the case of an employee leaving for whatever reason is not your concern. Also, somebody at the company hired you so they certainly can hire your replacement.

Especially if you give notice, if the company will not start to search for a replacement it's a problem for them. Besides you can't negotiate the pay of the new employee: if their offers are too low even if you endorse someone and personally write a reference this doesn't mean the candidate will accept.

Employees tend to see themselves as productive and a integral part of any organization. Should they leave, they feel as if their departure will spell doom for the past employer.

Such statement is false. Despite our desire to feel important, we're not. A company can go on without us and we shouldn't feel obligated to "help." They will do fine without you, as painful as that is to swallow. You should do as you shall do to do what you need to do to get where you need to go.

If you feel you must, go ahead and ask your manager if there's anything he/she would like you to do before you leave. My advice is leave behind a nice doc for the next person with any sort of gotcha's, username/password, or whatnot.

You're never responsible for your company being unprepared for your leaving. Don't let guilt stop you from advancing your career.

Your company will figure something out.

I'm going to go against everyone here who just says a flat-out "no, you are not responsible."

You mentioned that it's a small company and many startups have crumbled from this type of thing.

It isn't right for the company to put you in this sort of situation, so you can probably leave them to their fate, guilt-free.

However, if they expressed in advance that you would have such a crucial position, then the ethical thing to do would be to be upfront about intending to leave (you don't need to give too much detail), and hopefully you can work together to smooth the transition in a way that works out for everyone. If you signed up for a critical role and bail, then yes, you probably should feel bad about possibly ruining multiple businesses.

In an ideal world, every company has room to increase their "bus-factor", but in reality, contrary to most of the other answers, that can't always be accomplished (or may have been considered during risk-management and found to be the less optimal route).

※bus-factor: Number of people that can be hit by a bus before your company/project is completely screwed.

EDIT

I figured out what the key themes seem to be here.

Answers and commenters don't seem to think that OP has any influence on the world or those around them.

Yes, I acknowledge that there is also a false sense of importance that many people fall into:

Despite the fact that they could quit on Friday and be replaced by Monday.
But this is a small business,

with clients who depend on OP for their OWN deadlines. OP has significance. OP matters. Some of you might matter too.

Fun exercise, think about what might actually happen if you quit tomorrow.

Another key theme seems to be that people here suggest that OP lookout only for their own personal interests.

It IS possible to act in the interest of someone other than yourself. Believe me, I did it once and it didn't ruin my life.

Yes, it is completely reasonable for you to leave without having found them a replacement. You acted in good faith, you tried, they have rejected your attempts, the results are on them.

You might however try again in the vein of "what if I got run over by a bus/won the lottery?". Say you feel queasy about being such a company bottleneck, the lone resource in an important area. And that you need help, because you probably do. But don't even hint that you're thinking of leaving, since management already sounds a bit short-sighted, they could easily march you out the door in a snit.

Something else you can do to soothe your conscience is to work hard on documentation before you quit. See if you can clarify the code with some well-placed explanatory comments. If they end up hiring someone who even has no overlap with you at all, they will be utterly grateful. And it might be even more useful than any oral instructions you can impart since the effects will be more long-term.

Given the circumstances, is it reasonable for me to leave without
finding a replacement for my position?

I think it's reasonable. This isn't your responsibility.

That being said, how much do you value your relationship with this company and do you want to maintain that relationship after you leave? If the answer is yes, then it might make sense to inform them of your plans and let them know that you'll assist them in any way you can in finding your replacement.

Your employer has chosen to not have a fall-back (for whatever reason) when you are not available. This is shortsighted and could cost them.

What would happen today if you leave for lunch and get into a car accident - leaving you unable to work for several months? What happens when you go on vacation?

There is an old saying:

Your failure to plan in not a crisis on my part.

What can you do?
You've already tried to bring in someone else. Beyond that, system documentation should be complete. Someone will be taking your place after you leave - having documentation will help them transition.

It is definitely reasonable. You, as an employee, are not responsible for the continuity of your employer's business. It is not your problem if they fail to see the implications of their main developer leaving. Depending on your notice period, your employer might have enough time to hire someone and have them brought up to - a certain - speed by you. If you really care, you can discuss this when you hand in your notice and discuss this in a productive way with your employer.

But remember to set certain limits for yourself in regards to your employer trying to persuade you to stay longer in case no valid replacement can be found, etc.

Most answers so far see only parts of the whole.

Legally speaking, you have no obligation whatsoever to look for a replacement or, in fact, do anything at all to ensure that the company survives your departure. That is all very clearly a management responsibility. They should be prepared for you suddenly not being there, not just because you could exit the company but also because serious accidents are a thing and you could disappear for months or forever with no warning at all because of one.

Morally speaking, it is a small company that relies on you and will most likely be hit hard if you leave on short notice. Typically, the right thing to do would be to give them notice as early as possible, but from your question you have reasons not to do that. In such case, doing the next best thing would be morally right. Document everything well, make sure you don't have to leave early the days between giving notice and actually leaving, making things as easy as possible for your replacement and the clients, and the company.

Career-savy would be to burn as few bridges as possible. We have a saying here "you always meet twice in life", and in the business world that can be very much true. This is especially true about your clients. If you have a personal relationship with them, i.e. they know you by name and any troubles they would run into if you suddenly leave would be connected to your name in their minds.

Especially this last one is a responsibility to yourself that you definitely do have.

A lot of answers here say no. It's not quite that simple.

Once you've given notice, it seems completely reasonable to help the company find your replacement. You've said that you're the best person for that task, so why wouldn't you spend your notice period trying to ensure an orderly transition? You will be asked to, and refusing to would serve no purpose.

Do you have a responsibility to do this before your notice period? No. It's good that you've tried to subtly orchestrate matters such that the company has a head start on the replacement hire. But that's, to a degree, above and beyond, particularly as you'd have to announce your impending departure in order for everyone to actually understand what you're trying to do. Of course they won't find budget to add another you, while you're still there.

If you don't have to and/or plan to work a notice period at all, then all bets are off, and I can't help you, because this is always going to be a disruptive way to leave a business. Perhaps legal in your jurisdiction and with your particular contract, but not very pleasant for any of the people involved.

Can you set up an internal wiki for company knowledge? Can you start dumping your knowledge into it?

I did this in a past job after an employee left who'd been there for years. Any time somebody asked me a question, I said, "Look in the wiki." If the answer wasn't there, I put it there, or asked them to.

In your case, you may not get asked these kinds of questions, but you can make it part of your daily job: "How would I know how to troubleshoot this? How would I know where to find this?" Etc. Any time the answer isn't "I can find it in the wiki", put it there.

If you start doing this, you can leave with your conscience salved, because you're leaving them your knowledge so the next person won't be floundering.

In the spirit of not burning bridges, it would good to help your soon-to-be-ex employer find someone to take on your responsibilities. It shouldn't, however, be your responsibility to drive the process. It also shouldn't gate your departure if a suitable candidate isn't found before your leaving date.

Am I responsible for finding my own replacement?

Not really. As simple as that. They would not (i suppose) tell you "get ready" in case they were planning to fire you.

Unless you work as the hiring manager at your company, it's not your responsibility to find your replacement. It wouldn't make sense - as a developer, you should be good at developing things. Nobody could reasonably expect from you that you are any good at finding candidates, picking a good candidate, and hiring them.

And if your company told you that you were responsible to find your replacement, that's something you would do during your work time, so you couldn't do all the other things you are supposed to do in a day.

I think you should think of it the other way around. I assume you are about to sign a contract with a new employer and have a short notice time with your current employer. Why not inform you next employer about the situation and suggest that your current employer might ask you to stay a little longer than your notice period to hand over your work to your replacement and that you therefore, if possible, might delay the start with your next employer and/or would appreciate some flexibility at your new work the first month or so.

This way you could assist your current employer with finding your replacement (feel free to play a little game with your current employer "hmm, I am gonna be superbusy the period you ask about but just because I appreciate working with you so much I will make an effort and assist you with finding my replacement") which will improve your relationship with them, while you, at the same time, signal to your new employer that you are a reliable person that won't desert them in the future. Win-win!

The "standard" notice period is two weeks, but for many positions, that is incredibly short. Imagine an NFL player announcing in the middle of the season that they're retiring in two weeks. While you are not obligated to stay on indefinitely until you find a replacement, you do have a moral obligation to extend your stay some time past two weeks if you can't find a replacement. Depending on the role, that could be as long as a few months. The argument that the company should have planned around the possibility that you would leave because, after all, you could die at any moment, doesn't hold water. A fire could break out and destroy their headquarters; that doesn't mean there's nothing wrong with intentionally burning down their headquarters. There are many positions where planning around the possibility that an employee could be gone in two weeks would be incredibly onerous and would create ridiculous inefficiency. Although, if a company does find themselves in such a position, they should get a formal commitment, there's a certain degree to which there's an implicit commitment.