He will most likely join M$ if the board does not resign, because there is no better move to him then. But he leaves time to the board to see it, adding pressure together with the empoyees. It does not mean he is bluffing (what would be a better move in this case instead?)
All the employees threatening to leave depends on him actually becoming a Microsoft employee. That hasn't happened yet. So everyone is waiting for confirmation that he's indeed an employee because otherwise it just looks like a bluff.
People are waiting for the board decision. It is in Microsoft's interested to return Sam to OpenAI. ChatGPT is a brand at this point. And OpenAI controls bunch of patents and stuff.
But Sam will 100% hired by Microsoft if that won't work. Microsoft has no reason not to.
