Put yourself mentally in the position of whichever fan base were to be stuck with him as their new HC...can you imagine the message boards blowing up in enthusiastic anticipation of what's to come? Hardly. You know they would be freaking out over what such outsiders know of the Bills this year, in a bad way.
He still needs to actually prove he has what it takes at this level, and for too many times this year, talent/injuries notwithstanding, he simply couldn't get it done for whatever reason. That said, he's been on an upwards trajectory since Josh came back, and I think that he therefore does deserve to come back next year and prove he was better than appearances all along. But to jump from this year to a HC job? Bloody unlikely, IMHO.