When you buy a virtual digital copy, you are actually only buying a license to watch it (or read it or listen to it in the case of ebooks, audiobooks, and music.) Which means that yes, they can pull it at any time. If you own a physical edition, it’s yours; you can keep it or sell it or give it away. Sometimes it’s possible to download a copy of the virtual work to store on your own device, which gives at least a little more permanence.