If West Virginia does leave the Big East, and moves to the Big XII, the remaining teams in the Big East can add an additional non-conference game. For teams like Syracuse and Rutgers, adding another FCS opponent probably makes little sense, given both already have one scheduled.
Solution? Apparently playing a conference opponent in a non-conference game. Not unheard of, as Colorado and California met this year (was scheduled when Colorado was in the Big XII); Michigan and Michigan State met a few years back in basketball, twice, with one being a non-conference game.