Zimmer retiring/resigning wouldn't be a complete shock because of his health and the disappointment of this season but firing him wouldn't be smart IMO. The defense went back to being great after a poor start and he's still one of the best at player development.
People criticized his "run the ball" comments but I think that was more so to get the ball in Cook's hands rather than him acting like a dinosaur. It also could've had something to do with his QB's turnover issues. If there was some sort of issue with Cousins and they got rid of Zimmer because of it then it would only make the Cousins signing look even worse.