I wouldn't be so sure Tommy couldn't go 12-0 in the regular season in 2012. I'm not saying he definitely would have, but with the defense we had it certainly was very possible. Look at the games we played:
Navy - It was a slaughter in essentially all 3 phases of the team, no problem here.
Purdue - We only scored 2 TDs and a FG prior to Tommy's drive for the FG. Tommy scored 31 and 38 in his 2011 and 2013 meetings with Purdue, I'm confidant he could have matched Golson's 17 points in this game.
Michigan State - Tough defense, and Golson played well here, but we also only surrendered 3 points to the Spartans. Tommy was 2-0 in his other meetings with the Spartans, I'm confidant he would have scored more than 3 points if he played in this one.
Michigan - No question, he played most of the game here and ran in the only TD, so we can skip this one.
Miami - Again, we were firing in just about all 3 facets of the game here, and Miami only scored 3 points on our defense. Easy win even with Tommy (Who crushed Miami two years prior in the bowl)
Stanford - Iffy game here. Golson didn't have a particularly bad game, but wasn't particularly great either. He ended with a QBR of 21. Tommy was 4/4 on the winning drive in overtime. Tough to say how he would have fared over the course of an entire game, but it was certainly winnable for him.
BYU - No question here again, since Golson was out for this one and Tommy took all the snaps.
Oklahoma - This one is a bit of a question mark among the regular season games. Golson played pretty well and added 64 yards on the ground. He may have fumbled the ball once, but ended up recovering it. Still, the defense only surrendered 14 points to the Sooners, so unless Tommy turns the ball over a bunch (Which is unlikely since we only needed 25 passes from Golson to win this one) I think he could have scored more than 14. He scored more than 14 in 2013 despite all the turnovers. I think at worst we would have won the game 23-13, taking the TD off the board that was a result of the long pass to a young Chris Brown.
Pitt - People will point to this game as a game Tommy wouldn't have come back from, but Golson struggled so much for 3 quarters before he had to mount a comeback. We only had a pair of FGs on the board prior to the 4th, that's pretty bad offense. Our defense was fighting the flu too, but they came up with a stop when we needed one.
Boston College - BC only scored 6 points, Tommy would have won here.
Wake Forest - I don't need to say anything.
USC - This was the Theo game. Golson still threw for 216, but only needed 26 attempts in this one. Again, Tommy would have only needed to score 14 in this game to win, and Tommy was 2-1 in games against USC in his career. He probably should have been 3-0, but he took that hit in 2011 when we were mounting a comeback, Crist came in briefly, and it was all downhill from there.
Would circumstances have been different with a different QB under center? Sure, but the backbone of that team at the end of the day was still the defense. Some things would have changed, but when you consider Tommy faced some of the toughest defenses in 2012 and put us in position to win, I'm pretty confidant he could have scored enough against the other teams with that 2012 defense backing him up. At worst I think we would have gone 11-1 with the question mark probably being the 2012 Pitt game since it wasn't a great game offensively at all and the defense was legitimately sick.