Well most of the teams who would likely want to trade for him would be destinations he'd probably be fine with - Houston, Denver, Chicago, Arizona. Crud places like Cleveland, Jacksonville, etc. are not. So it's a moot point about him then retiring. Plus Romo would likely let Dallas and the team trying to trade for him know well before if he would go there. Any team trading for him is going to want to talk to him and his agent about a restructure before a deal is consummated. So this silly idea that he's going to wake up and have a text from Jerry saying "Sorry buddy, I traded you to Cleveland" is laughable.
So again it gets back to the basic point, if you can get something for him in a trade, one would be foolish to say no and just let him walk for nothing. Smart fans understand that.