Without even getting into tie breakers, if the Bills finish with 7 losses we would need the following: Steelers, Broncos, and Bengals all lose 1 game to get to 8 losses. And one of the AFC South teams (Jags, Texans, Colts) lose 2 games to get to 8 losses. Some of these teams play each other so some of these losses are guaranteed.
I'm sure there are other paths (Browns go 0-3, more AFC South losses allows for non-afc South teams to win out, tie breakers), but this to me is most likely and easy to understand. I'll worry about tie breakers in final week (if necessary).