I think they are going to let him finish the season, then "retire"; I don't like this scenario at all, because it won't give the new DC a real chance to evaluate the talent on the defense. They can't all be bad - look at what Pittsburgh is doing with their young guys.
If this is what Harbaugh is thinking then maybe he should pack his shit too because your job as an HC is to win football games period so you are going to choose your friendship over losing this team completely?