So if he eats her, would that mean world peace?

No? Yoru was already eaten by Chainsaw man however long ago (we didn't see just heard from Makima) . War has no power since being ended by Chainsaw man, and that why Yoru wants to end Chainsaw man because of stripping her of power. If anything she just lost the little fear she has left.

ohh got it, thanks for explaining to me!