The one that finishes highest gets the guarantee, the other one gets thrown in the pool of other candidates (would never get selected over another big AQ school in reality). NIU won't jump Fresno unless they lose, nor should they. I don't think NIU wins out, they haven't won that convincingly at times this year.
http://www.bcsfootball.org/news/story?id=4819597
No more than one such team from the non-AQ group shall earn an automatic berth in any year, unless non-AQ teams finish both No. 1 and No. 2 in the final BCS Standings. (Note: A second team may be eligible for at-large eligibility as noted below.) If two or more teams from those conferences satisfy the provisions for an automatic berth, then the team with the highest finish in the final BCS Standings will receive the automatic berth, and the remaining team or teams will be considered for at-large selection if it meets the criteria.