Well, that's my point really. The "storied programs" have fan support outside their alumni only so long as they are "relevant" and winning (with the possible exception of ND). But, a top tier program can go through 4-5-6 mediocre coaching hires and find that base eroding, rather quickly, and if HS kids forget who they ever were, they become like Minnesota.
The the spiral starts - unable to recruit, unable to attract top tier coaches, unable to sustain fan interest, and attendance, and money, and mediocrity beckons.
If not mediocrity, a label as being a pretty good program that is not top tier, a program that will be 9-3 on year and 7-5 the next. Three decades is my rough guess of how long it would take.
If Michigan for example in 2047 still had the most wins, but only one or two NY6 bowl game appearances, 5 or more losing seasons, and a lot of 7-5 seasons, they in my opinion would have dropped, and part of that would mean inability to recover because of recruiting.
That's the thing so, they have to totally whiff for a very long time. The have the resources, both tangible and intangible, to cover up any mistake they make. Michigan made back to back bad coaching hires, haven't won even a conference title in 14 years (2003 I think?), but they can afford Harbaugh, and that helmet attracts Harbaugh (or something similar if he hadn't been available), and a staff of top paid assistants, and it's like they never skipped a beat.
Flip side, MSU misses on some kids, has one bad year, coming off 3 Big Ten titles, another CCG appearance, a CFP appearance and a pair of BCS/NY6 bowl wins, and it totally undoes those 6 years. And they can't afford to go flip their whole staff like an OSU can and simply bring in a Wilson/Schiano duo because CFP semifinal losses aren't good enough.
So hypothetically, sure. But some of these things are so ingrained, that to think UM could miss badly, with the resources they have on like 20 straight years, and that MSU could overcome the odds to be on top for 20 straight years, or whatever, that to me it's like wondering if UM would vote to drop football all together.
Then mix in that because of the ratings they draw, they will get every benefit of the doubt, it's hard for them to really fall. See Michigan getting an Orange Bowl over MSU in 1999 or a Sugar Bowl over MSU in 2011. There's just too much momentum in one direction for me to believe at this point that things could reverse for a long enough period of time that these things would ever really change.