If Altman takes all of the good engineers and researchers with him, OpenAI is no more.
So the board can be the boss of nothing, sure, without the ability to do anything - leading the organisation, raising funds, and so on
Perhaps they could hire someone that could replace Sam Altman, but, that would require a much larger company who have the employees indifferent to the leadership, like, EA or something
OpenAI is much more smaller and close knit.