 Can demons be eradicated? They can be killed. Yes, they actually can be, but not by human. They have to be killed by an archangel. And that's the only way that you can't, that that's the only thing that can kill them besides God, Jesus. How do they kill them? Um, they, uh, they do battle in a different realm of existence. That's neither in the dark or the light. And it's old fashioned battle.