The mod is called Rhye's and Fall of Civilization. Without Stability, where is the fall? That is the primary purpose behind Stability. Besides that, Stability also allows for Civs to rise from the ashes. With Stability, there is a dynamic feel to the game that allows for more realism.
I have seen this argument before (someone said to me "what empire ever lasted forever?") and while I can see the point, I also respectfully disagree. Not all realism in the game is fun. There are many examples of completely unrealistic things in Civ that are there because otherwise the game would not be fun. For example, a ship can take decades or even centuries to go from one continent to another. Great persons can live for centuries if we don't use them. Europe is larger in the RFC map than in reality.
While I agree that secession can make the game more fun, I think that, also for the purposes of fun, it should be easier to avoid in the game than it is in reality. Or at least more controllable, or predictable. It's just too frustrating to conquer a city, invest on it, make it a jewel of a place, and then lose it just like that, without any kind of warning, along with two or three like it.
Also, while huge empires may not last all that much in reality, it's just so much fun to build them, it should be at least
possible to do it in the game. Maybe it should be hard, but possible. Actually, it seems like it is possible, but only if you know how stability works well enough, and many people seem not to.
Just as a last note, I am not complaining here. I am deeply grateful for the mod. I wish I had the time right now to help working on it. This is just in the spirit of constructive feedback.
Cheers,
Rodrigo