Because of the history at Georgia Southern, unless they can't financially make it work I think they stay. Their attendance did not boost with the move up but have gone to bowls regularly and are better than at least 25-30 or so G5 programs out there right now.
As for App and Citadel, do you really want to smack talk a team who owned Citadel? App won that series 19-7 with just a 3-point loss in last game, so it was not some big blowout. App was in transition and most of the team did not care. If you are bragging about one game in a series where App owned Citadel and was 7 years ago then call Charter or get help somewhere lol.
In 2019, App was a top 20 ranked program (https://www.espn.com/college-football/rankings), beat 2 P5 teams, and became the 1st and only former FCS team to win a bowl game every season after completing a move to FBS. They are 5-0 and have pretty much owned CUSA and MAC in bowl games. App is not a P5 caliber team by any means but I think you can safely say Boise State, UCF, and App are the top teams who moved up from I-AA/FCS. They are one of the top 3 G5 programs in the country right now. I don't remember seeing Citadel ranked in the FBS polls like App, NDSU, JMU, etc have pulled off receiving votes in them while in FCS. I believe App was the team that forced the change to that rule to even allow it. In fact, where was Citadel ranked in the STATS or Coaches Poll this year? I can't find them?
You guys had a down year after being ranked in the top 10 every year...oh wait I believe that was Furman and Wofford who have run the SoCon about every year? LOL.
Outside of the FCS, the sad part is that NDSU is the only team that is considered relevant right now. Nobody at FS1, ESPN, etc. really pays attention to the FCS and I wish they would because there is still some good football, especially at the top of the CAA, Big Sky, and MVFC.