I'm resigning from the startup that I work at on Monday, giving the US-standard notice of two weeks. I am the sole developer on one of the platforms that our product supports, to the extent that no one else at the company even knows the programming language that I develop in. This arrangement is reasonably typical of startups, from what I've seen.
I've already handled documentation within reason, but again, no one at the company will be able to use it at a high level without quite a bit of studying. Typically, the notice period is used to transition to a replacement or to teammates, and I've watched this work very well on slightly larger teams (3 or 4 people) but I don't have the latter, and the chance of finding the former within a day or two (so that there would be time to transition before my last day) is roughly zero - even if we did find someone, they'd likely want to give similar notice at their current position anyways.
What should I do or propose once the transition period begins? What should my manager (or the CEO, or anyone, it's a startup!) do?