It is going to take 3 or 4 straight years of good teams for the "casual" fan to come back with consistency. I think even a 2001 or 2007-like season on its own wouldn't bring fans back consistently.
Ironically, I remember when the Memorial Stadium renovations happened and there was a lot of criticism about the associated lowering of capacity. Imagine how empty Memorial Stadium would look today if it still seated 70K. I know there were some initial discussions during the renovations about what to do with the horseshoe, I would argue that it should be "squared" off and the current 9,800 seats reduced to probably 2,500 or 3,000. Capacity with the horseshoe cut down to 2,500 seats would be 53,480, which honestly feels about right with current attendance trends. The great thing about such a plan is if trends ever reverse and attendance starts shooting up again, the University can then expand the horseshoe back to 9,800 seats or even more if necessary.