^He's right. Other profiles on your XBox can access the content just fine. Using your hard drive on another console to play the game on another profile would be a problem though.
As far as when games are taken off the Marketplace, I believe you can still redownload them IF they're in your Download History. I've heard many people say they were able to. I'll try it out; I deleted the amazing Yaris game to clean up some space but I can try to redownload it.