system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40k] If the Tyranids devoured all organic life in the galaxy outside themselves, would the Chaos Gods die? What about if the Necrons eradicated all organic life?
gpt
Yes and yes.  The Chaos Gods are basically made of emotions - they're the aggregate Warp presences of uncounted trillions of sentient beings.  Lose the sentient beings feeding emotions into the aggregates, and the Chaos Gods vanish.  The collapse of the Imperium alone would starve Chaos, as humans are its main food source - Orks, Necrons and Tyranids don't feed Chaos, and Eldar and Tau are too few to matter.

(Fun fact: according to at least some Daemon Primarchs, Chaos *has already won*.  The state of constant war and misery that is the Galaxy in 40k *is* the win condition for Chaos, because it provides maximum emotional energy for the Chaos Gods to fatten on.  Stalemate is victory.  If Abaddon's Black Crusade actually destroyed the Imperium, Chaos would go down with it.)