Maybe it's the last "Go for it season" and after the season ends, AB is gone (if he even makes it through the season) and more importantly, Brady retires. I could see Gronk coming back for the last hurrah. They could afford to wait til half way through the season to actually sign him (Gronkowski) to the active squad.
Bills just have to do their thing, get better, and shoot for the playoffs, one way or the other. 2020 may finally be the year the AFC east is wide open. Go Bills.