Musk fired most of the engineers. I'd be pretty surprised if we see the level of attrition at OpenAI getting within an order of magnitude of that. We are just making predictions, though. I could be way off the mark and many more people are willing to jump ship than I imagine.
As for Microsoft, if they let OpenAI go, then what? Does Google pick them up? Elon? They are still looking to invent AGI, so I'd be surprised if no one wants to take advantage of that opportunity. I'd expect Microsoft to be aware of this and weigh into their calculus.