I honestly think in the case of an interception, the play is whistled dead immediately. If the intercepting team is ahead, game over. If not, then change of possession.
I've never seen a case where the defender doesn't take a knee or fall down. But I think the play continues until they do. My guess is that Auburn will be the first one to benefit from this lucky reprieve of the defender fumbling it back and letting them score a TD.
At the risk of re-opening old wounds, stranger things have happened.