My housemate grumbles about getting rid of her DVD collection from time to time. I told her that she's not allowed to get rid of her Dogma DVD. I even watch it once in a while.
USB DVD readers are pretty cheap and backing up a DVD movie to a file (either just the movie as mp4/whatever or the whole disc with menus, special content and all that jazz as an ISO) is trivial. DVDs themselves are fragile circles of plastic that store data a micron-thin foil layer that can be hurt by too spicy a laser pointer. Do yourself and your roommate a favor and make a copy of that thing for posterity's sake.