Nobody is going in midseason. He wouldn’t be able to hire assistants, can’t install an offense or defense, and anybody who left a program to join him would be marked for life. He wouldn’t be interviewing behind Saban’s back so I’m sure Saban would give his support for staying through the end of the season.
I wouldn't mind a look at Dan Mullen. When he had a good QB and good players he had good offensive ideas and found ways to find playmakers. I think his downfall was more with running the entire team rather than just his best skillset which is offense. Not sure if he'd be interested in the job or where he's at right now.
Other names I like:
Kirk Ciarocca - Minnesota
Ryan Grubb - Washington U
NIL and Transfer Portal likely keeps both out of the HC position(s) in collegiate football in the future. I know O'Brien doesn't like the idea of being a head coach in this era. I've seen numerous comments on how Mullen feels about the state of college football as well and they mirror O'Brien's.