“…Why leave the board if a buyout was imminent?”

Why not? An argument that says he’s leaving because he no longer needs to provide input and opinion *because* a buyout is imminent is just as plausible. However, I don’t have a clue one way or the other. But I am curious as to why someone would give up a board position, unless it’s for health issues. After all, it’s not nine-to-five, five-days-a-week, and not particularly onerous even for someone as old as many of us.