I've made regular internal and external backups of pictures, home movies, and personal files like Quicken and TurboTax for years. The picture and home movie files are already over 400 GB. So adding GOG download backups to the list has been easy to implement.
One backup is to one of three internal 3TB hard drives. Then every couple of months I make a backup to an external hard drive and rotate it with the backup hard drives stored in safe deposit boxes at two banks that are located far apart.
Really important files also get backed up more frequently to Blu-ray discs, DVDs, and/or USB flash drives. In the future I will be making these backups to M-Disc Blu-ray discs which should last much longer than regular Blu-ray discs.
With EMPs being in the news lately I may start wrapping the external hard drives in layers of aluminum foil and insulator before storing them at home or in safe deposit boxes.
I realize this may be a paranoid reaction, and for game backups it probably is. But if I'm using these techniques to save one-of-a-kind photos, home movies, and personal files, I might as well add in GOG games.
P.S. This paranoia stems from my grandparents losing all of their one-of-a-kind family photos and personal records in a house fire about 50 years ago, and my sister having a similar loss when her house burned down about 15 years ago. Living in the center of tornado alley doesn't help with this issue!