first off, as ridiculous as it sounds, yoru's plan is such a great metaphor for humanity's never-ending bloodlust, chaos and violence.
second of all, if death is gone and the world is turned into chaos like death said, wouldn't there even be more devils? not to mention, is it even possible to use denji-chainsawman to erase death in the first place? nuclear weapons still got reinvented even after chainsawman ate it anyway :))