My thoughts on some of the replies...
Freeze would be great, but I don't think he's going to leave Liberty for anything other than a HC position.
Joe Brady would be grand slam hire, but word is, his desire is to stay in the NFL and work his way up there. He's only been there for a full season, and he's already a hot commodity in the league.
I'd think Kendal Briles and Jeff Lebby would be looked at if Saban decided to go the college route (just a guess).
RE: Gase and BIll O'Brien... They certainly fit the mold that, IMO, Saban is looking for. Both have college and NFL experience. Both are respected offensive coordinators. Both have been head coaches (O'Brien in both CFB and NFL). Both have connections with Saban, so there aren't really unknowns in terms of how they'll mesh. Gase has been on Saban's staff (many moons ago), and O'Brien has been a visitor to Tuscaloosa a couple times over the years to share ideas (was a speaker at a coaches clinic too I think). Gase has also been a visitor in the same capacity. Not saying either will be hired, but I'd bet both get a lot of attention. The one knock that I've heard for a while on O'Brien is that he can be difficult to work for, but in this case I don't see that as an issue since he isn't the head guy. Anyway, Saban sets the tone in that building (and regardless, he's difficult to work for himself). Also, it is believed that Gase will have OC opportunities if he wants to remains in the NFL.