It's not happening in any millennium. There would be no reason for Harbaugh to coach again in the NFL. He has the best job right where he is at and it's not changing. He has total control and doesn't have an owner or a GM to answer to.
IMO Harbaugh has always been a college coach and that is where he shines. He does not work well when he don't have complete control.
Don't get me wrong because I like me some Harbaugh but the reality is he is a college coach, not a NFL coach.