Will users still be able to get the game from their download history? And will it automatically kill the game centre multi player setup? Thanks.
If you remove your game from the App Store users will still be able to get it via their purchase history. I have removed a number of my games from the App Store when I sold the rights and I can still get the original versions via my purchase history. I don't use GameCenter in my games, so I can't answer that.
Does it really matter? If you're pulling the app from the app store you're saying 'It's not my concern any longer'. I would guess it would stay in Game Center as the App Store and Game Center are 2 different services. I don't know the answer because I haven't had a reason to pull any apps.
You should know too that if you're going to pull your app from the app store, you'll never be able to use that app name again -- at least that's the way it used to work, unless something changed.