> Isn't there a good chance they'd just mothball the whole company and keep on making regular gasoline-engine cars?

All of those companies - and the entire industry - are investing heavily in their own electric cars; some already have announced dates when they will stop production of gas engines IIRC. Depending on the price, of course, I imagine they'd love to add Tesla's prestige, patents, and maybe their talent.

My uneducated guess is that's how Tesla will end, a division of a major car-maker. When did GM last add a new brand? Imagine the bidding.