If he's fired now the current board can offer him a severance package that may not be on the table once Elon takes over. Might be a good thing, or strategic?
This is the correct answer, Elon will not be as generous when cutting numbers.
I'll never forget letting go of staff in France and Italy. The employees were overjoyed we were letting them go and got into fights over who would be taking the packages. I learned that they received 1 year of salary upfront tax free with a bunch of additional benefits to help with job training and placement.
An average middle manager friend has had this happen 3 times, each time after a US acquisition. He now has a chateau in the south of france and is very happy with himself.
Severance packages are usually a deal: company pays you $X, and you agree to say (or not say) certain things, and also agree where you might work in the future (i.e. not at a competitor). The current board/CEO may want to keep things stable, and offer generous money to keep things on an even keel; Elon may not care what a former executive says or does.
Why wouldn't it be? The sale hasn't finalized, so unless there's evidence that they're intentionally harming the company they can continue to operate as usual.
