>I'm talking about single player games.

This means nothing, there have been piles of single player games that have required a connection check before working. Sim City 4 was an example of this.

And, even buying it and not having that check doesn't mean that it won't be updated to require a server (you have an actual disk to reinstall right, because the original installer may disappear too).

Many modern games that have only a single-player mode are still intentionally dependent on the servers staying up, and games that have both single-player and online modes will prevent you from playing the offline mode if they can't connect to the servers.

You can still play Quake 3 and Unreal Tournament (1999) online, because third-party game servers used to be the normal way online games worked. Hell, Team Fortress 2 is only playable on third-party servers, as the official servers are full of cheaters.