I wouldn't want Cotton trying to be OC and O-line coach again. That is just too much and IMO you can't do both without one or both not getting all they attention they deserve. Plus, back in '03 Bo wasn't planning on keeping Cotton as OC, he had Lane Kiffin lined-up. Bo obviously likes Cotton as an o-line coach though.
If Watson left I'd tab Gus Malzahn from Tulsa.
Ron Brown could be a heck of an OC, awesome football mind, but his ministry obligations take time.
But I'd say Watson has a significant amount to prove before any good jobs would come his way, he should be here a while longer.