Khorne would be incomprehensible even if half the universe found peace, and destroyed planets

Black Crusade: The Tome of Blood pg 19

"The Lord of Battle dreams of one day wrapping his scarlet fingers around Slaanesh’s soft, delicate neck and crushing it until the younger god’s depraved screams of pleasure become shrieks of agony and then finally go silent with a satisfying snapping of godly bone. This is not his only dream. Khorne is eternal. As long as man has murdered his brother, wolf has hunted prey, and planets have been consumed by the death spasms of their stars, Khorne has existed. Until such time as all these things cease, he remains.

It is impossible to vanquish Khorne completely, since the very act of fighting against him gives him strength. Only through complete apathy can sentient races hope to even so much as lessen the power of the Blood God. Khorne knows this. While his power would remain unfathomably great even if half of the universe’s civilisations found lasting peace and serenity, it would still be diminished, and Khorne is a jealous god who does not suffer loss well. This need to keep his power, and to grow it, motivates his actions. Each skull taken, and each drop of blood that fills the rivers and lakes of his realm, is a physical testament to the power of Khorne. With grim satisfaction, the Blood God can cast his gaze about his realm and know that his strength is undeniable.

He can also literally watch as his power waxes and wanes. When the tides of blood retreat from the shores of the blasted realm, Khorne’s rage becomes nearly uncontrollable. At these times, the galaxy trembles in fear. Long dormant Warp storms blaze with hellish light, churning and spitting raw Chaos into space. Nearby planets are cracked in two from tendrils of malice that reach out from the void and strike them like a Bloodthirster’s whip. The astral forms of Farseers travelling the webway are vaporised in rushing currents of searing rage"