I don't think that's the case. There's no amount of money that Microsoft could throw at Sam to convince him to sell. Not only is he already wealthy, but he's also a true believer in AI. And unlike Snapchat, it's going to be very hard for incumbents to clone.
We forgetting how Dall-E 2 was made irrelevant just a few weeks after release by Stable Diffusion?
I agree with everything else you're saying though, I don't think he'd have any interest in selling it.
Every experience I ever had of people who achieve power and success tells me that you are wrong. His own wealth is irrelevant. His beliefs are also not relevant. It is very likely he will want to "take the next step". He can always use that next shit ton of money to invest in the next big thing in AI.