Ian Rapoport: Sean may not have a team lined up.

Wrong. He had 3 years left on his contract when he "retired" and he now has 2 years left. Coach contracts are not like player contracts.
Coaches contract are governed by The NFL Constitution and arbitrated by guess who? Roger Goodell. His word is final. I linked this information on a prior thread. Unless they somehow get the case moved to a public trial.