When Cleveland lost their team, their fans had 8 games notice. The stands were wild, wild scenes. Back then, CBS and NBC could avoid showing most of the crazy behavior to the nationwide audience. But i bet the NFL remembers how crazy it got, and that it was not a good look for the league.
This time, the drama and chaos would be going on for multiple years, and we have the internet. No way the NFL wants a piece of Bills fans when a move seems in the cards.
I still say they're staying.