Let's pretend there are no more upsets this year (which ain't gonna happen) - in which case Bama, ND and Ohio State have all punched their tickets to the playoffs. And to be honest, OU getting upset looks a lot more likely than any of those 3 teams.
We'd have to jump Clemson, which is not necessarily impossible, for the 4th spot, as the ACC is looking fairly wretched. Their big win vs. A&M is looking like fool's gold as the Aggies squeaked by a crap Arkie team today (after getting steam-rolled by Bama, which could arguably mean Clemson would also get steam-rolled by Bama....but who wouldn't at this point?). With Duke losing today Clemson has no more ranked teams on their schedule; meanwhile we have an improving Horns' team, a TCU team that could have beaten tOSU, Bedlam (pokes are down but the instate rivalry will get some hype), an always dangerous Tech offense, and then UWV twice if we are going to get to the playoffs. If both OU and UWV are undefeated for the last game of the year and OU wins then we conceivably jump Clemson, but that's still a tall ask for us to leap a team pegged at #2 to start the year and often mentioned in the same breath as Bama. We'd need style points, like a better margin of victory over TCU than tOSU had.
Put a fork in the Pac12.