What I see there is that if you have a NC HC, you have to keep him. Plain and simple.
You have to keep the Pete Carrolls, Urban Meyers, Butch Davises, Steve Spurriers, Nick Sabans, etc of the world if you expect to go on winning and winning.
Yes, at the risk of their becoming Les Miles or Mack Brown, etc. And who's to say those who stagnated a bit, but weren't bad - wouldn't have had future peaks?
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Whether it's due to the NFL, health, or whatever, if you don't hang onto your NC HC, you're not going to continue winning NCs.