Mike Leach does not qualify for the College Football HOF on 1 of the criteria. 0.600 win percentage. His is 0.596. If he'd won 3 more games he'd qualify. In fact he probably hit 0.600 halfway through the season.
But the HOF has a special review process for unique cases, so he may be considered. Kinda like (iirc) Chris Lofton deserving to have his jersey retired but not technically qualified per UT's reqs.
Anyway, 3x Conference COY (2x Pac12, 1x Big12). 1x National COY. Has more (18) wins as an unranked team over ranked teams than any other coach. Broke school offensive records at UK, TTU, WSU, MSU that are still held. His players broke conference records at all schools. His coaching tree is breaking records all over the place.
His coaching tree is possibly more successful than Saban's. Just off the top of my head: Heupel, Lincoln Riley, Kliff Kingsbury, Sonny Dykes, Dave Aranda, Neal Brown, Holgorsen, Wes Welker, etc.
Saban's got Jimbo, Kirby, Kiffin, Napier, Muschamp, Pruitt, McElwain, Locksley, etc. Lots of guys who got fired, several guys (Like Kiffin and Butch Jones) who are only under his "tree" because of stints at Bama. Not because they came up through his program as a player or GA. That's an argument for another day.
Leach's offense, and his impact stretches across football at every level. It's changed the way the game has played. Leach would get in the HOF (I think) via a review committee as a "special case) for the impact he's had on the sport. Not on his coaching record alone.