The Bills defense never missed a beat after he left, since he was replaced with Bernard, a markedly better player whose name you actually hear during games.
The Bears also added lots of other players on their defense, actual difference-makers like Montez Sweat , and that's what is making the difference, not Tremaine Edmunds and his weekly disappearing act. Go look at the rest of that draft and see how much the Bills blew it by trading up and wasting a 1st rounder on him.