Yes this is very true, but, maybe some specialized weapons designed to flood the soul with some type of energy to extinguish the souls. Or maybe someone else could come up with somthin better than my idea. This idea of souls has happened in Black Ops with the rituals, but this would be a full on soul encounter with some sort of a bigger creature that is harder to defeat in so many roundsThis would be the Zombies mode. I think it has already happened in a few Zombies sections in either WaW/Black Ops 1, 2, or 3.
But it is an interesting concept. However, what would we kill these souls with? We aren't Ghostbusters in the game, ya know.