for example I imagine Supercell would be shitting itself at the idea of having to keep the servers open indefinitely for its long list of failed follow ups to clash of clans.

Stop Killing Games (as an initiative) isn't asking for servers to be kept up indefinitely. Adding a "vs bots" mode (if one doesn't already exist, never played clash of clans) or allowing P2P connections to let people keep playing would suffice.