Wondering is one thing, but the insistence on it after Hoke and Brandon have both commented on it is kind of odd. And Sam Webb, who is himself an insider with a really strong track record believes its all Hoke.
FWIW, I know Hoke a bit although I am not privy to anything specifically relates to this, and I don't see why anyone would think he is incapable of firing someone. As an assistant, he saw a lot of staff changes. As HC, he has made plenty of changes, going so far as to have a purge at Ball State. And, a lot of people think him and Borges had some kind of super unbreakable bond, which is silly. They are both professionals. And they have been together for only 5 years. The most important think to recognize is that Hoke would probably give his life to win at Michigan, so a coordinator is no big deal.