Based on a thorough reading of Romo's contract, the Cowboys cannot issue him the franchise tag if no deal is reached by the end of the 2013 league year. Therefore, he'd be a free agent if there is no new contract -- giving Romo added leverage.
The interpretation has been confirmed by sources with in-depth knowledge of the language.
Here's why Romo would become a free agent: He technically has three years left on his current contract. Based on paragraphs 27 and 28 of the deal, however, the final two years of Romo's contract void with no action necessary from either party if he's on the Cowboys' roster by the end of the 2013 league year. So, if Romo still is on the roster at that time, he's a free agent.
That's when a team usually would issue the franchise tag.
Yet all of that occurs after the franchise-tag window has closed. So the Cowboys could not use their tag on Romo.
If the void happened during the franchise-tag window, Romo could be tagged. But it won't, so he can't. Not that the Cowboys won't try if it comes to that, but sources believe it won't work.
Romo as a free agent? It will happen if no deal is done. That's one reason the Cowboys want it done sooner rather than later. In addition, they are holding off on other business until they get Romo's finished.