I have roughly guessed that it takes 30 years of mediocrity for a helmet to drop. Borderline near helmet programs can drop faster of course. So, yes, I think Michigan could be one more coach away from dropping, if they don't have some rather successful seasons soon. You can't just poke along at 9-4 and 10-3 forever, obviously, because most upper level programs want more and will fire a coach who does that, and the crap shoot starts again.
You need some top ten finishes, some playoff appearances, some conference championships, etc.
Fundamentally, I agree with you that Michigan (or any "helmet" with the current exception of ND) *COULD* drop. Unfortunately, however, I think that we are farther from witnessing that glorious day than you seem to believe.
In terms of NC's Michigan is now 20 years and counting from their last one. That isn't good for a helmet, but it isn't awful and Michigan previously endured a substantially longer NC drought.
In terms of conference titles Michigan is now 12 years and counting from their last one. That is REALLY bad for a helmet. Compare to the last time the other generally agreed upon helmets won a conference title:
- 2016: Bama, Oklahoma
- 2014: Ohio State
- 2009: Texas
- 2008: USC
- 2004: Michigan
- N/A: Notre Dame
Here is the last time each of the generally agreed upon helmets won an NC:
- 2015: Bama
- 2014: Ohio State
- 2005: Texas
- 2004: USC
- 2000: Oklahoma
- 1997: Michigan
- 1988: Notre Dame
Michigan is clearly light on "hardware" as compared to the other helmet teams over the past 12-20 years but I believe that it takes more than a lack of hardware to lose helmet status. It takes a fall from relevance.
Since Michigan's last conference (2004) and national (1997) titles they have:
Top-10 finishes:
They have also been ranked in the top-10 a lot more frequently than that and they have played two enormous games that got major national attention:
- 2016: A #3 v #2 matchup against Ohio State with major playoff implications for both teams and, by extension, a whole bunch of other teams.
- 2006: A #1 v #2 matchup against Ohio State with major BCSNCG implications for both teams and, by extension, a whole bunch of other teams.
My point is that while Michigan clearly does not have the level of hardware over the past 12-20 years that we expect from a helmet team, they haven't sunken into long-term irrelevance. They have continued to have a periodic presence in the NC discussion and finish ranked and in the top-10. When Michigan goes 20 years without finishing ranked in the top-10, we'll talk. Until then they are a helmet.