If he's reinstated, then that's it, AI will be used to screw us plebs for sure (fastest path to evil domination).
If he's not reinstated, then it would appear the board acted in the nick of time. For now.
For a nonprofit board, the closest thing is something "the members of the board agree to resign after providing for named replacements". Individual members of the board can be sacked by a quorum of the board, but the board collectively can't be sacked.
EDIT: Correction:
Actually, nonprofits can have a variety of structures defining who the members are that are ultimately in charge. There must be a board, and there may be voting members to whom the board is accountable. The members, however, defined, generally can vote and replace boards members, and so could sack the board.
OTOH, I can't find any information about OpenAI having voting members beyond the board to whom they are accountable.
OpenAI does not have an associative body, to my knowledge.