Jacksonville is not the only city having trouble selling out their games. The Vikings signed Brett Favre in part because they needed a way to drum up sales. Play-off contender San Diego has also experienced problems selling all their tickets. In the past couple of years I have had no trouble buying tickets to games in such such stalwart NFL cities as San Francisco and Kansas City.
I have attended pro football games throughout the South and if the team is anywhere from mediocre to bad it is no problem to get seats for any game. When Tampa was horrible they rarely if ever sold out and unless the Dolphins are really good then there are often plenty of seats available in Miami. In New Orleans I once bought seats on the 40 from a scalper for face value. When I was in seminary the Falcons had a buy 1 get 1 free sale for a game against an NFC champion Rams team that was called "the greatest show on turf." This was normal in Atlanta where fan loyalty runs first to the Georgia Bulldogs and then to everyone else. In Jacksonville, loyalty goes from Florida and FSU and then down to the Jags. The reason people assume the Jags are about to move is because many NFL people believe that Jacksonville does not deserve a team.
The people who run the NFL tend to view its component parts as things to be exploited. They exploit players through use of non-guaranteed contracts and they exploit fan bases and cities by threatening to move in an effort to wring concessions to get more money. The NFL has shown no problems leaving cities with long football traditions like Cleveland, Baltimore, and Los Angeles. The only way to fight this is to exploit the league right back. Every city that I mentioned above would be fine if they no longer had a team. I don't doubt the feelings of grief would immense but the cities would survive.
That is because the cities have been able to deliver diverse offerings of activities to people with different interest. These cities could develop these diverse offerings because an NFL team gave them the aura of being "major league." Since Atlanta got the Falcons they have become a major international city. The Falcons could close up shop tomorrow and Atlanta would be fine.
What Jacksonville should do is quit worrying about the Jags leaving. Right now use the existence of the Jags as leverage to develop diverse attractions. Miami can ignore the Dolphins and be fine because of what South Beach offers. New Orleans often ignored the Saints and didn't care because they have the French Quarter.
The years of the Jacksonville Jaguars parallels the years I have been gone. When I return it is easy to see that Jacksonville has changed and it is no longer a provincial backwater. I am sure that having the Jaguars is a major impetus behind the development. I hope the city leaders of Jacksonville seek not to grow with the Jags but grow beyond needing the Jags.
I guess what I am saying is use the NFL because they sure will use you.