Yeah, but they did that with Ware because they had no choice. They couldn't manage his cap number any longer and kicked that can down the road as far as they could. (Though I'm sure some number cruncher will still try to claim otherwise).
Romo's number isn't good for a backup, but based on how little they're paying Dak, it's affordable to have both guys. They could keep him if they truly wanted to, and they can sit on the contract for months until somebody makes an acceptable offer.
And if Tony can or chooses to threaten anything, so can Jerry and the Cowboys. If he wants things to get ugly, they can get ugly. But that's not what anyone wants and I don't expect it to happen.
But this is a two-way street here, not simply what Romo wants.