Unless they are absolutely crushed by the Gamecocks, of course. I just don't see TCU jumping them, and when you look at wins against the current BCS Top 25, Auburn has 5 victories, while Oregon has 2, TCU has 1, Stanford has 1, and Wisconsin has 1. Not only do I think that Auburn is already in, I think they should be in. Take care of business, Ducks, because Oregon-Auburn would be one of the better BCS title match-ups since Texas-USC.
Auburn can't play in the BCS title game if they lose. They made the rule back when Oklahoma jumped in after losing their conference title game. You have to at least win your conference to play for the championship.
I did some digging, and you are right. There is no rule stating that you have to win your conference to get in. BUT, the formula was changed to favor the human polls more than the computer system. If Auburn drops to only #3, then yes, the rankings could put them #2. But, I still think that Wisconsin would get more votes than Auburn at that point. If we were going to play a 1 loss team, I think it would be the Badgers.