We were the number 1 seed with home field advantage in the playoffs and would have played Green Bay regardless of whether or not Romo came back when he was healthy.
So this debate only boils down to whether or not we would have won the GB game with Romo playing QB instead of Dak. Dak played a very good game, threw for over 300 yards, 3 TDs, had over a 100 QB rating and we scored on 6 of our 9 possessions. He threw an interception though.
The assumption is Romo is the better QB so then he MOST DEFINITELY would have had a better game. Perhaps he would have but I know of 2 instances in the same game where the offense played better in a game with Brandon Weeden than we did with Tony Romo. Those games were against Washington in 2014 when Romo missed some time in the game and Weeden came in for 2 series. We scored 7 points with Romo and 10 with Weeden. Romo replaced Weeden and our offense sputtered again while we lost in OT. The second time was against Philly in week 2 of 2015. Our offense scored 6 points in 3 quarters with Romo playing. Weeden played the 4th quarter and threw a TD pass. So the better QB doesn't always play better.
There is also the assumption Romo was just going to light up the GB secondary because of injury. He had a chance to light up the Giants banged up secondary in the playoffs in 2007. We had torched the Giants for 45 points in game 1 and 31 points in game 2. We scored 17 points on our first 4 possessions so we were well on our way to doing the same thing. Then we were held scoreless on the last 4 possessions of the game even though we had open receivers because the Giants secondary was pretty terrible due to injuries.
There is also the assumption that there is no way Romo could fail at the end of the game. We were carving GB up in 2013 all game until the end when Romo threw 2 interceptions on back to back drives. We were carving up Denver in 2013 when Romo threw an interception in the final 2 minutes of a tie game when all we needed was a FG to win. We were carving up Detroit in 2011 when Romo threw a couple of pick sixes and we lost the game. Even when we are cruising against a team, Romo still possessed the ability to make mistakes. We can't just assume he plays mistakes free football that day because he's the better QB.
I bring up those examples and surely Romo diehard fans will rush in to defend him and point out things like pressure, dropped passes, and the defense, etc. But they just can't bring themselves to look at the GB game in 2016 and extend the same courtesy to Dak. They just refuse to do it. I just don't understand the obsession with harping over a "what if" scenario in which we replace one of the very best performers we had on the field that day with another player and assuming that was the key factor in the outcome of our season ending loss. Dak didn't play perfect, but neither would Romo have.