If he left, it would only be for a team that is already very good but needs a QB. Is there such a team in the NFL like that?
A few maybes....
Brees is a free agent....so maybe Saints.
Denver is close and needs a QB.
Colts aren't sold on their QB and are decent.
Steelers have a pretty decent team. If Ben can't return, I could see that.
Tannehill is a free agent. If Tenn doesn't extend him, I can see BB swooping in and signing him. (BB has a history of signing players that have given him trouble e.g. Welker) Then Tenn turning around and signing Brady.
But if NE can add a couple of FA WR there is a very decent chance they will present him with the best opportunity for a 7th ring.
I think Dallas is more than a QB away.