Good luck.
You'd need new legislation to have any legal case (for future games obviously). There aren't laws that entitle you to access to the servers forever or for the game to work without servers.
I'd be all for "you must release all necessary code (or at least all the technical details to replicate the interactions) to replace the server when you shut it down, or make the entire game fully playable without server interaction", but even writing those laws in a comprehensive way would be hard, let alone getting them passed or enforcing them.