All of Musk's companies have a reputation for being really sucky places to work. Interesting, but poorly paid, authoritarian and very long hours. It's suffering you accept to learn stuff and then leave, I've heard it described. Not a place to have kids.
Meaning Musk cannot rehire anyone who's left these companies.
No true scotsman fallacy aside, firms make this mistake all the time and have to rehire the star/legacy maintainer at contractor rates to keep things running.
But worst case...
These firing decisions are not irreversible! If you accidentally fire a 10x programmer, you can re-hire.