There are a couple of problems with that scenario: Romo is due huge money next season, so it's hard to trade him with that contact. The only way he's likely to get traded would be if he's willing to re-work his deal. He's not doing that to go someplace he doesn't want just because you want a 7th round draft pick. And he can always just decide to retire rather that let the Cowboys screw him over in an attempt to get a backup - you think any team would trade for a guy who says he's not going to show up? Then there is the fact that Jerry would look like a complete *** for forcing that issue, especially after the way Romo has handled this, when the team really has no leverage other than Romo's competitive nature.
Romo's contract is extremely trade friendly.
The recipient of Romo would merely have to take on his $14mill salary in 2017, none of which is guaranteed, so aside from losing whatever draft compensation that team gave up, they could easily walk away from Romo at any time with no cost (although I think they may have to guarantee a veterans salary if their on the roster for game 1). Romos salary in 2018 jumps up to $19.5mill but as I said, none of it is guaranteed and if Romo is performing at a top 10 level, his compensation would be considered under market.
Given the terms of the existing deal, its a no brainer for Romo to renegotiate his current deal with any future team as it would likely give him guarantees + money up front.
The issue with trading Romo in the off season is that it results in a $19.6 million dead money cap charge that gets accelerated to the 2017 cap plus they lose a helluva backup QB.
Cap gurus kindly correct any errors I may have made please