So just throwing mud at the wall a bit.
Bob Stoops is the interim (only 61 and was coaching last year in the XFL I think if they wanted to go with him though they wouldn't have made him interim, still he's going to have a say in who they pick) so with that being said I think that puts Heupel low on the list.
A few other names in the Stoops Coaching Tree
Mike Leach - OU is an upgrade over Miss State, and the fact he's now shown some ability in the SEC will be a positive.
Bo Pelini - Nebraska firing this dude was a huge mistake and has set them back and I think he's far enough removed from that falling out to be an option. (probably low on their list)
Kevin Sumlin - I mean he had success at Houston & Texas A&M, rough go at Arizona, but many coaches have gone there and done poorly. I think his ties to Stoops help and the fact he's very familiar with recruiting that region.
Mike Stoops - Long shot I know but maybe we're looking at the wrong brother? (I think this would be a bad hire and think they'd take everyone else on the list before him...but he is his brother)
Jay Norvell - I'm baffled why his name hasn't come up more, 33-26 at Nevada and making chump changes. OU assistant from 2008 to 2014
I know USC & LSU went and got big names for big money, not sure if OU has the pull to do that or if they even want to. But not sure who Stoops would be wanting to see there either...