I think at the end of the year, a 13-0 OSU of course won't need to argue SOS, and a 12-1 OSU who still wins the B1G won't either. The most likely 12-1 would be a loss to UM, horrible as that would be for their fans, but it's very survivable in terms of the playoff. The Pac 12 is obviously back in the picture with two one loss teams.
Clemson is the team most liable to a 12-1 record being left out, if they say lose to USCe. A 12-1 SEC champ is going to be "in". If every conference champ is 12-1, I think the ACC gets left out. If Clemson is 13-0, then there could be 4 12-1 conference champs and 3 spots, and that would be a mess.