We absolutely did lose that game because Romo choked. The defense might have gotten the stop. We don't know because Romo couldn't handle a basic football play when it mattered most, just like in the Denver game. Played great all game until the moment of truth, Then he choked and threw a blatant game ending pick.
Playing great but then choking the game away at the worst possible moment does not grant you the benefit of "we didn't lose because of him". It's the exact opposite. We lost specifically because of him.