Luckily there are some friendly people with eye patches and peglegs on the internet backing them up for you.
You might be surprised. Plenty of sites backing up whatever they can. Try archive.org and various abandonware sites.
Or, I might not be surprised at all. You might find Borderlands for the next 20 years, but what about the games that only sold like 40k copies to begin with?
In case of zombie apocalypse, your best friends will probably be a bicycle (to get away from the zombies in almost any terrain and road condition, not be without industrial fuel the next day, and be able to do needed repairs with rough tools and scraps that can be found), a hunting knife, and maybe a crossbow if you can find one (weapons that can be sharpened and reused, and crossbow allowing random joes to just make piercing sticks (again with scraps that can be found anywhere) that work like an arrow, again weapons that do not depend on industrial infrastructure that will not be available anymore). Games that need electricity would be extremely hard to use, it’s better to buy card decks that have multiple rule sets for different games to play, like french decks and tarot, maybe a tabletop set that also has multiple games.