What this game should do to increase longevity

[linay]

Not if each story was its own thing. Going back to my previous example. If you wrote a book about a political coop or existential threat set in India that was happened in the same time line as the US Civil War, how could there possibly be any unresolved plot points? Even if the main protagonist was American, there would be no cross over because the story you are reading occurs completely in India.

Many games handle story telling like this and it actually works incredibly well.

I'm thinking from the present state where there is an overarching story. If they manage to resolve everything, then we can start fresh.

That said, I also wouldn't like it if every expansion is self-contained with nothing to link from one expansion to the next. They can do it after every few expansions, but there should be continuation and even recurring characters and such between several of the expansions.