Re: geographically speaking
Realistically the Cowboys would be in the west and St. Louis or someone would be in the NFC East. But the NFL ain't gonna get rid of Cowboys/Skins, Dallas/Philly, or Cowboys/Giants.
Similarly, Dolphins/Jets, Dolphins/Bills, and Miami/New England are long standing rivalries that I seriously doubt are going anywhere. Since there are so few games played and the travel costs are relatively similar whether you are flying to Jacksonville or Buffalo, I don't think the NFL really needs geographical divisions at all.
I do wonder what would have happened if the Oilers hadn't moved. I miss playing Pittsburgh, Cincy, and Cleveland every year, even as the Texans. I would hope the NFL wouldn't screw with that division if we still had the Oilers. I guess you'd have to put Baltimore in the AFC South -- they belong as much as Indy, plus you have the natural hatred for the Baltimore fans towards the Colts (like Cleveland's for the Ravens).