He's not an exec, he's a founder (which together with Larry and Eric controls over 50% of shareholder voting power). He'd have to fire himself.

That's not entirely true. The board has the power to fire executives (that's one of the purposes of having a board, for executive oversight). You're correct in that those three could theoretically vote to change the board, but doing so also has other drastic consequences. That also takes time and process, and it's possible the board can make a move before they have the time to see that process through.