Also - "everything doesn't end" - the game does continue. It's just that you start getting fireballs (meteors?) hitting random spots every few turns (or is it every turn?). If they hit a city, the city and all its districts get destroyed.
I never saw this happen, but I suppose if you played an Apocalypse mode game to the point where fireballs managed to destroy all cities, maybe the world does effectively end. But you would also think that at the point where there is the cities (and units?) of only one civ left, that civ should just be declared the winner, I suppose domination if not other victory. Did anyone take a game this far?