Ah. Well kushites don't have siege engines besides the siege tower. They use elephants to destroy buildings. The only chance for no elephants to occur is to play on a medium or smaller map (which is the case) so that the chance that no elephant stables is placed is significant.
Gaia units are also ordered to not capture (otherwise they would stand around trying to capture houses rather than fight the enemy soldiers.)
It's not gaias task to end the game however, it's the players task.
But I recognize that this may end up in a situation where gaia is too powerful in order for players to defeat each other while not being powerful enough to end the match one way or another.
So I guess there should be an elephant stables at any time (PITA to implement with that CityPainter thing), or the wonder could spawn elephants too. I guess I'll try that.
Speaking about the CityPainter, the buildings must also be aligned with the path so that units don't become trapped, but I failed to implement it correctly and it increased the loading screen time by a minute (because its supposed to work with any kind of shape like circles too, so it has to test many points -.-)