If there are good financial prospects for one or both startups, and you can live for a year on your savings, and you have no other financial obligations, I don't see why you wouldn't take the plunge. Even if the startups don't work out, you will probably have substantially increased your skillset in a year.
2.) On the one hand, you shouldn't screw your current employer. On the other hand, if they can't find a developer after several months of trying, that's their problem, not yours.
Try to make the transition as smooth as possible for them, but don't stay just because they can't hire.