If I recall, the trigger NPC issue was (still is?) used in many mods. Modders found out that all civs respawned in a map if all had been killed. That's why on a few maps where you are supposed to battle enemy civilians, there is a cow stashed away at the side lines - cows are on the civilian team, and nobody is likely to harm them. So only when you killed the cow did the enemies rise again ;)