They don't have to provide a way to install the games in perpetuity, but I'm pretty sure the ToS don't provide a way for them to stop you from keeping or running a DRM free copy you've downloaded.

So sure, the ToS says you don't own the game, but unlike ubisoft that puts that non-ownership into practice, GOG goes out of their way to make that legal non-ownership utterly meaningless. If you have a copy of the game, then you have a copy of the game.

Back them up on a hard drive and their ToS doesn’t mean squat anymore. I guess that takes a little more effort and investment but if you want to own the game without DRM that will do it.

ToS doesn't mean squat here if the law says otherwise. It's insane to me that US has this the reverse.