The lesson here is that there is no sure thing except, perhaps, Meyer.Michigan:
Harbaugh is still head coach (for now at least). Taking a page from Tom Herman and Big Ed, Harbaugh recently canned a coordinator to save his own neck for another year--DC Don Brown.
Potential DC replacements include: Muschamp, Jim Leavitt (FAU DC), Derek Mason (formerly Vandy), Lovie Smith (formerly U of I; good defensive mind/crummy HC), Charlie Strong (see Lovie Smith comment); John Rudzinski (Air Force DC).
5 candidates for Michigan football defensive coordinator
Michigan Football: More strong options for defensive coordinator
Michigan fires defensive coordinator Don Brown after Wolverines struggle through 2020 season, per report
Harbaugh will likely have at least one more year to turn the ship around. But, if not, candidates to replace him include: Bieniemy (OC KC Chiefs), Byron Leftwich (OC Tampa Bay Bucs), PJ Fleck (Minnesota), Clark Lea (DC Notre Dame), Tom Allen (Indiana), Pat Fitzgerald (NW), Matt Campbell (ISU), Jeremy Chadwell (Coastal Carolina), Luke Fickell (Cincy).
As much as I like Campbell, if I was Michigan, I'd offer Allen or Fleck.
5 Potential Head Coach Candidates for the Michigan Wolverines
Michigan Football: 8 Possible candidates to replace Jim Harbaugh
When Harbaugh was hired, few had any doubt that he would succeed, and wildly. And probably less would have hesitated to hire him at Texas, certainly in front of Herman.
He may still make it at MI but I doubt it. I think his place is in the NFL.