I’d be fine with a minimum support time if an end of life date is not made clear when buying. Say a game has to be able to run for at least one more year after purchasing unless there is an explivit warning about the planned shut down date. That would at least seem reasonable to me.
Of course the optimum would be requiring either offline functionality, or, even better, enabling fans to host their own servers once the official ones shut down. That way games could be preserved for much longer.
But at the very least, people shouldn’t lose access after an unreasonably short time.