Gaming

Civilization is like a board game. It's over when you hit the turn limit.

Fighting games usually do have campaigns, of a sort. It's each character's story line. It can be over when you beat every character or if you go through every character's story (ie run through the main mode all the way through with each character you can play as).

Racing games also have campaigns usually, and some even have progression systems. But the campaign is just going through progressively more difficult races. They're complete when you've gotten the best rank on every track and/or collected every part.

They're all meant to be played over and over again though; often against other humans. These are also the types of games that come with a lot of options, settings and modes to facilitate playing the same game slightly differently and keep things fun. So I guess the real answer is: whenever you want. If you're playing then because they're fun they never have to end. If you're playing as a completionist, it's over when you've gotten all the achievements/experienced every piece of content you can access.