NFL

Whether or not the bills are in a seasonal slump or their window is actually closed remains to be seen, but that cannot be determined by one season alone.

You can infer based off of other factors though that they're likely looking at a soft rebuild if this season really does end in disaster. Their cap situation is terrible, they haven't been drafting particularly well, and many of their best players (Diggs, Poyer, Hyde, Miller) are on the wrong side of thirty. In other words, they're getting worse while teams like the Texans, Jags, and Dolphins have been getting better.

I don't think it's an exaggeration to predict that they won't be SB contenders next year, and probably not the year after that. Their window likely will be closed for that time, and they'll need to re-open it through smart drafting and FA signings.