"Startup fails" is the reason why these companies have the so-called "limited liability". They file for bankruptcy, founders get on with their lifes, investors see nothing. This is, in fact the vast majority of the cases, and the reason investing is called "high-risk, high reward".

Generally not, and I'm quite sure they wouldn't have to for this deal.

Obviously any exit event would be a valuation and Yuri would get a cut. But in case of failure, everyone walks away empty-handed.

All is a loss. Entrepreneurs are not help personally liable for the debt in this case.