The only way a Power Five Undefeated team gets left out of the playoffs is if all five or four plus Notre Dame don’t have a loss. Can’t happen this year because Notre Dame and the PAC 12 won’t be undefeated.
A one loss Clemson team might not get selected over a 1 loss Power Five Conference Champion. A one loss ACC Champion Clemson will not likely be left out of the playoffs over a one loss SEC team that did not win the conference. We got a pass for losing to Syracuse when Kelly Bryant was hurt, that year we were being compared to other 1 loss conference champions and a one loss Bama. I don’t think any Power Five teams were undefeated. If you get the crap beat out of you like Ohio State has the last Two years for your only loss, you might get left out like they did. Elite teams may drop a fluke game, but they don’t get stomped. If LSU beats a Tua-less Bama team by more than 14 the committee would have a hard time putting both Bama and LSU in the playoff. If LSU loses to a Bama team without TUA playing by even 1 point, they would need a lot of other teams to get upset in a conference championship game or they are Sugar Bowl bound.