I’ve seen it happen with two CEOs. With the first one, myself and some of the other Senior Mangers approached the investors directly and explained our concerns. Effectively a civilised coup. The CEO was replaced.
In the second case, the CEO went completely mad, kept sacking all his senior managers (7 CFOs in 3 years), brought the company to its knees and was eventually paid off very handsomely by the board and replaced, although the company was left in a pretty desperate state from which it is still struggling to recover.
In both cases they started off fine, seemed very rational and nice, but cracked under pressure when we had a run of bad quarters and then just stopped functioning and became completely destructive. Quite interesting to watch from the inside.