system
Given the following post, respond as if you're commenting on Reddit:
human
[40k/Warhammer] How do you actually 'kill' a Nurgle Plaguebearer or Marine?

Iv seen many depictions of either being shot or stabbed and then dropping instantly. I'm curious to know what is happening here. I get that they don't have regular bodily functions as they are demons or so corrupted to the core to make the distinction irrelevant, so how do regular bullets or normal metal edged weapons actually cause any fatal damage?

Not including epic heros or pskers, how does getting stabbed or shot by a bunch regular Imperial Guardsmen (while limited in example) actually bring down a being where their organs and internal physical makeup is essentially meaningless?
gpt
Plaguebearers, like all daemons, are never truly killed when they are slain in the materium.

Rather, maintaining a physical presence in the materium is itself a strenuous task for creatures of the warp. Damaging their physical body strains this manifestation until it can no longer be maintained, and they retreat back to the warp. Daemons often dissolve into a nondescript substance due to this upon defeat.

A chaos marine is still "mortal" in to the extent that space marines are considered as such. Hurt them enough and they die, likely returning to their patron diety's realm where they may or may not be put to use.