Yes, those cities did get another franchise after their team moved, but the smallest of those metro areas is Cleveland with 2 million, which is twice as much as Buffalo metro (1.1 million). Plus remember that Cleveland threatened the NFL with legal action to get another team.
Right now, the best bet for keeping the team here is the mysterious Kelly group (Golisano?, Jacobs?, Rich?), plus the political clout of Sen. Schumer, who will no doubt go toe-to-toe with Goodell if there is noise about moving the team. Even with those, there is still no guarantee of the Bills staying, or getting another team if they leave.