One will end up undefeated, get the auto-bid, and a first round bye.

The loser of this hypothetical B12 CCG, now with a record of 12-1, should get in over a 2 loss SEC, 2 loss Big Ten, or even a 1 loss Notre Dame (their 1 loss was to Northern Illinois). but the committee could consider Notre Dames recent performance and heavily discount their early season loss (to a team that should never even compete with them).

However, if the two teams in the B12 championship game are both 11-1, or one is 12-0 and the other is 11-1 and the 12-0 team wins, then the loser will be 11-2 after the B12 CCG. This is a harder sell to get an at-large bid.

BTW, Notre Dame has a decent path to win out: their remaining games are: Georgia Tech, Navy, Florida State, Virginia, Army, and USC. Holy Triple Option Batman... Doesn't Georgia Tech still run it as well as the Academies?

Assume the SEC and B1G both get three teams in... then you have the single G5 team, Notre Dame, the B12 champ, and the ACC champ.
That only leave 1 at large bid, probably given to a second ACC team or a second B12 team. Clemson + Miami? or leave one of them to take the 11-1 loser of BYU and Iowa State?

A second Notre Dame loss likely puts them on the outside looking in... leaving room for 2 teams from both the B12 and the ACC.