I remember in The U 30 For 30 there was a game where Miami went up huge on someone and ended up with a similar collapse. Jimmy Johnson (I'm pretty sure he was the coach for that game) said that he learned from that and would never let that happen again.
Also there's the story of one of the greatest college football coaches losing to.... Louisiana Monroe in his first season.
I'm not saying Harsin is or will be one of the greatest coaches all time, but if this has happened to others who are elite coaches, is it possible that maybe the sky isn't falling??