If a multiplayer-only game turns down official servers, and you can’t self-host within the game, they should owe players a separate server binary they can run, or a partial refund for breaking the game. It should not be hard, especially if it’s a known constraint when they develop the game.
The one MMO I’ve meaningfully played, RuneScape, has open source replicas of its server from different points in time, that the community has made. I’m not gonna pretend it’s zero work, but a developer with the source code absolutely could do these things. It also doesn’t need to be perfectly compatible with the original one, you can replace a complex DB backend with something standard and less performant. Only runs on Linux, or MS Server 2k8? The community of people who care will figure it out.
Maybe a source code release would be preferable in this kind of option. EA just did this with a few Command and Conquer games.