Does he still have that much cash? Would expect that SpaceX would have to cut if Tesla really needs money. I don't think Musk has much cash lying around that's not already in one of his companies.
Enough people believe in Tesla that they can certainly find a way to generate cash. As a WORST case scenario i’m sure another auto maker would love to recapitalize them in order to acquire their technology. Tesla actually going out of existence seems unlikely to me at this point.