Teams "figured" that before too, and paid the price when they were proven wrong about it. If Romo hit the open market, certain teams that could have traded for him would have little or no chance of signing him.
Due to Jerry's loyalty, he would only try to trade Romo to a team of his choice. Those exact teams would be the ones who would sign him as a FA. I would bet they would also not give up picks if they think there is a good chance of nabbing him.
Outside of Den, Arizona, Buffalo or KC........no one else has a chance at Romo whether he is traded or released.
Teams know this, so his trade value will be pretty low IMO. For example, let's say Denver wants him, they will not offer up much because they know that Tony would probably pick them over most if he were released. Cleveland could offer a 1st and a 2nd but if Romo says no.....Jerry won't send him there.
It would have to be a multi-team bidding war(of good teams) behind the scenes to raise the stakes.
I think Dallas will do all they can to give Romo a chance to start on a team of his choice.