Yep, that should do it. Like LJB's scenario, we're talking about OSU getting help by means of several upsets, rather than OSU being a lock as long as they win out.
My scenario actually requires very few upsets:
1. Alabama 13-0: beats Chattanooga, Auburn, SEC East champ - no upsets here
2. Clemson 12-1: beats Wake Forest, South Carolina, ACC Coastal champ - no upsets here
3. Wisconsin 11-2: beats Purdue, Minnesota, Penn State in CCG - no upsets here
4. Penn State 10-3: beats Rutgers, Michigan State; loses to Wisconsin in CCG - no upsets here
5. Oklahoma 10-2: beats #10 WVU, #13 Okie State - both tough games, but not upsets according to the rankings (Oklahoma is #8)
The only true upsets would have to come out of the PAC 12, where #20 Washington State would have to knock off #7 Washington. The game is a rivalry and will be played at WSU, so an upset here is not a stretch. For Washington State to win the PAC 12, they would have to upset the PAC 12 South champion (probably Colorado) in the title game.
However, if Washington State beats Washington, then it doesn't really matter which team comes out of the PAC 12 as all will have at least two losses. I believe that a one-loss Ohio State team with a great resume, lots of talent, an exciting style of football, and a huge TV audience will get in over any two-loss PAC 12 team.
The primary upsets that Ohio State has to worry about are
being upset by Michigan State or Michigan.
The Buckeyes doomsday scenario would be the following:
1. Alabama beats Chattanooga and Auburn, but loses to Florida in the SEC championship game. At that point, Florida (11-2) is in and so is one-loss Alabama (sorry folks, that's just the way it's gonna go).
2. Penn State (11-2) beats Wisconsin in the Big Ten championship game.
3. Clemson (12-1) wins the ACC.
4. Washington (12-1) win the PAC 12.
Under that scenario, Penn State, Clemson, and Washington are fighting for the final two spots, with Ohio State finishing #6 (again) in the final playoff rankings.