Well, I'm not that suprised that developers didn't include the possibilities that you decide to kill everyone in certain city in case of endings. If they had, that would have meant dozens of different endings, depending on which city you destroyed. Think about it:
- The normal endings to those two cities already present in the game
- Ending where you exterminated VC and didn't fix the reactor
- Ending where you exterminated VC and did repair the reactor
- Ending where you exterminated both cities
- Ending where you exterminated Gecko
And then, think the same formula to every city, town and village in game. And that's not only the endings, but then those should affect ingame situations as well, like the quest you may or may not get...
I would say, too big work for only small chance that someone actually goes for those paths...
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"As we all know, holy men has born during Christmas...
Like mr. Holopainen over there!"
- Marco Hietala, the bass player of Nightwish