I think there will be a decline. Certainly not the mass exodus we saw during Cata but WoW is growing older. Its been out what 8 years now? People are getting burned out especially when instead of making stuff more challenging they keep making it easier. I think one reason a game like Everquest, though a lot smaller, has held on to a lot of its veterans is because the content they release is always challenging and they dont dumb it down so Average Joe can do it. When games become too easy they become less fun. Dont believe me? If you play Madden or other sports games edit all your player stats to be 100 and then turn down all the computer AI. Sure you will beat teams by 100 but after a few days its just boring. Adding games like pokemon and challenge modes isnt going to keep players around. Those are geared towards casuals and they are the ones that will leave a game usually before the dedicated veteran will. Keeping more content relevant is the only way to keep more players around. Adding more BG maps, at least one per major content patch, will keep more players around. Adding a bunch more dailies that are boring as hell to grind out isnt going to keep people around.