GoG is very much about the marketing of game preservation. That said, to my knowledge, they (like Steam) don’t remove it from your account. Just from the store. So if you bought it, you can still play it.

GoG is a bit better in that their DRM model only requires you to authenticate to download, not reinstall. So you can theoretically archive all of your purchases if you have way more storage than you should. But it also is horrible at surfacing when an installer has an update so… mostly this is only viable for truly dead games.