Point is he loses credibility if the board doesn't think he's actually going through with joining Microsoft and using it as a negotiating tactic to scare them.

Because the whole "the entire company will quit and join Sam" depends on him actually going through with it and becoming an employee.

I see it the other way, Satya has clearly stated that he'd hire Sam and the rest of OpenAI anytime, but as soon as Sam is officially hired it might be seen as a door closing on any chance to revive OpenAI. Satya saying "Securing the talent" could be read as either them working for OpenAI, for microsoft or for a microsoft funded new startup.

I'm pretty sure the board takes the threat seriously regardless.

OAI cares more about the likelihood 90% of the employees leave than what Sam does or doesn't do.

The employees mass resigning depends entirely on whether Sam actually becomes a real employee or not. That hasn't happened yet.

But MS has said they are willing to hire Sam/Greg and the employees have stated that they are willing to follow Sam/Greg.

If you think that Satya will go back on his offer argue that, but otherwise it seems like the players are Sam/Greg and the board.

You make it sound like Prigozhin’s operation.