babarian34: What are you on about, I just installed Metal Gear from GOG offline installers and it works perfectly. The game has just returned to the GOG store, too.

That being said, yes, back up all of your gog offline installers, it's the only way to give "ownership" and "DRM free" meaning. If you rely only on gog hosting in the cloud it's not much different then steam in the end, incl. the risk of loosing your games or unwanted changes to the installers.