This precisely correct. The board hires & fires the CEO. End of story. When the board is unhappy how the company is being run, their recourse is to...fire the CEO. What is unusual here is the wellspring of support from "the troops", such that if they stuck with their firing the CEO, there would be hardly any company left to be BoD of! The board didn't understand the depth of employee allegiance to sama.
I saw a claim at the time that a handful of employees rallied everyone else to sign the letter and post support on Twitter. Between that and Altman reportedly having a vindictive streak, I'm thinking the actual employee support was paper-thin.
Prisoner's dilemma and/or social pressure when million in profit share units hang in the balance. Joining MS was a way to stop their compensation being at risk by being stuck on a sinking ship