Alan is extremely well respected at Google. I seriously doubt Sundar had anything to do with it. Alan has effectively been retired for several years now (ever since he took a hiatus to work on the stratosphere jump).
I don't disagree with your point. To clarify, I was stating that it's expected to hear people leaving following a decrease in responsibility; I was not trying to imply that such change has been necessarily involuntary. It could very well be the other way around, in fact, i.e. a reorg happens as a result of one's intent to retire in the near future.
Yeah. That makes sense. I guess demotion makes it seem like it wasn't his choice. I would slightly change your statement to say "he had effectively resigned ever since he took his initial leave of absence."