Last I heard, Elon Musk was very cash-poor after his two divorces. Most of his money is tied up in equity stakes in SpaceX and Tesla.

So if Tesla fails, then the "personal guarantee" simply turns into SpaceX shares. And SpaceX is a pre-IPO company.

He still didn't have to do that. It's more about signalling his confidence level. I wouldn't bet against Elon.