Frazier made the Bills into a top 3 defense multiple years running with a regular season consistency that is rare.
He failed, repeatedly, in the playoffs. Part, or a lot, of that blame (and praise) rests on the head coach. We fans have no clue where those nuances lie.
On another note, taking a sabbatical does not mean lounging by the pool or playing xbox. He's looking at options.
He is well liked and well respected, as far as I can tell.
He'll become a head coach soon.