I think it will be Watson. If reports are true that he's clearly outshining Sanders, it will be an easy choice. First, Sanders seems so mild-mannered that he will merely put his head down and keep working. He'll toe the line with the "best for the team, all I care about is winning" cliché ... so that part's easy.
It's not hard to imagine Watson performing better with no pressure and nothing on the line anyway. It may be just enough to convince Browns brass that one last shot at lightning in the bottle is the right move.
If he falters or gets injured, we can finally close the book on this terrible saga, with the last chapter taking place on the field.
It's not what I want, and for that reason it's exactly what I expect to see.