system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer] How much should a Daemon fear true death?

While in most every case, a defeated Daemon will just reform in the warp and be ready for another go however many years later it takes for the Daemon to reform in the achronal madness of the warp; sometimes a Daemon can be confronted with actual complete annihilation; never to return or exist again in any form.   Such as M'Kar whose daemonic essence was completely burned out when he was defeated at Maccragge or Aghalbor by Vulkan.  

Yet the sources I can find on the subject never seem to delve into how the prospect of a final, irreversible death and the obliteration of consciousness is seen by a Daemon.   If a Daemon knows that it picked the fight with the wrong person and its true death is imminent, how would it respond?  Trembling fear and pathetic begging to be spared?  Rage?  Denial at the idea that it can die forever?
gpt
I don’t think they ever go into the POV of a demon. We can get hints of how afraid they are of it in Master of Mankind.

The Emperor personally goes into the Webway to counter attack a demon horde. Just the sight of him terrifies them so much that some just run away right there. 

I can only assume that because the Emperor is called the Anathema by Chaos, he has the ability to give demons a true death. We know he accomplishes it at least once when he kills Horus.