In a response to a post from the AntiDRM Twitter account, Ubisoft Support has clarified that users who don’t sign in to their account can potentially lose access to Ubisoft games they’ve purchased. The initial post from AntiDRM featured a snippet of an e-mail sent to a user from Ubisoft notifying them that their account had been temporarily suspended due to inactivity and warning that it would be closed permanently in 30 days. Responding to the ominous e-mail, the Ubisoft Support Twitter account stated “We certainly do not want you to lose access to your games or account” and noted that account closure could be avoided by signing in to the account again.
GOG comes close by allowing their users to get an installer if they want a back up.
Correct, GoG is completely DRM free and has the ability to download offline installer packages for all your games. There are even a few scripts out there to do it for you.
Some of Steam’s content does as well, but not all and it’s hard to tell.
GoG is no longer completely DRM free, one example is the Hitman games that require online connection to play.