If steam goes under, a significant portion of your steam games won’t launch anymore, period. If GOG goes under, you can still use 100% of their installers, provided you still have them backed up. No, they are not going to be able to do that step for you. Did the store you bought physical games from put your discs in storage for you, so they wouldn’t clog up your basement? Did they give you a new copy if you lost or threw out your disc and then changed your mind?