If Rex puts Tebow in it would be viewed as a last ditch effort type of move. It would stink of desperation. If it failed (and it likely would) I think he would be toast. If he isn't already.
If I were Rex, I would stick with Sanchez, and hope for the best. Try to eke out a few wins, try to pin the losses on injuries and hope that he can hang on for another year.
The Jets owner seems like a real moron.