Sharalyan is still around. You have to remember that there were two Sharalyans. One is the main City-State which we can see on the world map and the other was an island nation created by Sharalyans and also named Sharalyan. The island nation is the one that was essentially destroyed, the main City-State still lives on.

Aside from that, ARR is the base game that all players must complete. Expansions are just add-ons that has add content for various level ranges but still require the player to play the base game. It's how almost all MMOs work.