There seems to be a lot of confusion, myself included, about Microsoft delisting underperforming games on Xbox Live Arcade. It seems that even though a game will be delisted from the service, it won’t really be removed entirely, just thrown in a sort of “back room.”
According to Aaron Greenberg, Director of Product Management for Xbox 360 and Live has stated that this is the case and that if you own one of those titles and you delete it and decide you want it later, you’ll still be able to re-download the game. Multiplayer and leaderboards will still work as they always have and delisted titles can still be purchased through the tell a friend option. So don’t worry too much about it, but it still sounds like a hassle to me.