I heard from local sports radio that people close to Rex say he's not coming back to the NFL as an assistant/D-coordinator and if he's not given another HC gig, he apparently has a lucrative TV offer lined up. I believe every word of it.
At this point in his career, can anyone really picture Rex as a D-coordinator? He would be a larger character than any HC and would overshadow any HC pretty much just b/c of his persona - not a good dynamic, IMO.