Face it: if Final Fantasy XIII suffers the same divide FFXII did, the series is over. It will go the way of Tomb Raider, Army Men, and whatever else, gradually being unsold and eventually canned. The secret’s out-people aren’t happy with Final Fantasy’s direction. Final Fantasy XIII is the series' last shot if it doesn't turn itself around.
It won’t be immediate, after XIII there will be more games, XIII very well could be the stab wound that causes the most bleeding.
Here are a list of items that need to happen to ensure the series doesn't tank. Check it out at OCModShop.