If Oklahoma State wins out, especially against Oklahoma then this whole thing is moot, however in case they don't:
DO NOT HAVE LSU AND ALABAMA PLAY AGAIN FOR THE TITLE.
First of all LSU already won the game between these two. Should Alabama get another shot? If they do, and the Crimson Tide wins should they be national champs with both teams having identical records and each team beating the other once? Of course not! If the Tide were to win and they were declared co-champs, then the "championship" game doesn't really decide the champion.
The biggest reason not to repeat: They both have great defense but really mediocre offenses! Keep in mind that neither team could score even one touchdown against each other, something Penn State did, Oregon did, even Kentucky did, against those teams.
A great game would be Okla. State's offense against LSU's defense, but if that doesn't happen (due to a loss by Okla. State) then the matchup should still be a great offense against a great defense. Assuming LSU doesn't fall apart in its remaining games it should be the championship defense team. The championship offensive team should be either Oklahoma (only if it beats Okla. State) or Stanford. While Oregon already proved its offense is more potent than Stanford's, most of the same reasons there should be no LSU-Alabama repeat apply to an LSU-Oregon repeat (except that Oregon has a great offense while Alabama doesn't). The reality is that LSU would probably shut down Stanford but at least Stanford would score a touchdown or two.
The darkhorse: Houston. If it wins out, with Case Keenum at the helm, the Cougars should get their shot on the big stage.