You pose a good question. There are many ways that it can be implemented and of course it depends on the game. Have a solo/offline mode, replace online multiplayer with local multiplayer or direct connect (for games like Among Us), release a dedicated server (so groups of people can start their own.
At a minimum, it needs to be better than "Could not reach game server, please check your connection and try again." The standard we could hold companies to would be through each province's consumer rights agency, but would have the legislation properly behind their efforts.