Short answer: Brent Venables.
Long response:
First, I don't see a coaching change coming until late/after next season (if it happens). IF Hart could and was inclined to go nuclear and do something before signing day 2017, I think there's only one person out there who's available and would even have the potential to flip our recruiting board. That's Chip Kelley. If you're not going to hire him, then there's no reason to make a change until the Fall.
Once the time comes, futile as it will be, the first thing I think the new AD has to do, and do it publicly, is to follow the advice of Clay Travis, Cowherd and others and back the dump truck of money up to JG's front door. Do not under any circumstances allow for any lingering doubt in the mind of this fanbase that we could've had the rockstar. It will not be fair to the new head coach or the fanbase to leave any trace of doubt on this matter. Hold a presser, shut it down, and move on.
My #1 is Venables. His body of work makes it clear that he can spot talent, develop talent, and place that talent in the best position to succeed. He knows how to recruit this area and the SW. Has publicly stated that he will not take on a rebuilding project, which means we couldn't wait to let the program crater again before pursuing him. It also means that if he accepted the job, we are ready to take the next step. Dave Aranda and Lincoln Riley are the other coordinators I'd look to. I think all three of these coaches will be HFC at P5 schools soon. They are the cream of the crop and I'd consider any one of them a home run.
I don't see much in the way of current P5 head coaches that I'd pursue. We're not flipping Jimbo or Jimmy Frank. If by some miracle Stoops or Gundy is available, they'd be on my list.
I'm leery of the non-P5 ranks after what happened with DD. That said, I'd look into Scott Satterfield.