Fire = chance of lawsuit

Layoff = severance (to avoid the lawsuit)

Quit = neither

It's obvious which one Musk would prefer.

sometimes quitting voluntarily can give you better severance than forced layoff

How does that work? Do they make an open offer to everyone if they quit they get $x?

That can happen, but people tend to call that a voluntary layoff.

yes, though not exactly sure how is it beneficial to company, maybe then they are not obliged to follow stricter rules for mass layoffs, if they can lower the threshold of leaving people