I’d go with a simple proposal: if you use the word “buy” the seller is required to refund buyers if the seller’s action removes access (unlike, say, losing access to a CD or DVD after the disc is scratched).

The most likely outcome is that they’d change their storefronts to use the word “rent” but that’s a good outcome (it encourages buyers to accurately understand what they’re paying for) and it would allow other options like releasing an old game without DRM prior to killing servers.