To further discussion, we have sadly unilaterally decided that in fact that these Demons are beyond redemptions... simply because we have no ethical dilemmas in exterminating them. While this maybe true in many (all) canon respects, I would be remiss if I didn't postulate a
much beloved counter theory that the Doom Demons are merely "aliens" who are indistinguishable from the Demonic hordes that predominate much of our religious and supernatural imagery of "Hell" and other negative afterlifes.
Now I know what your saying... get that Doom 2005 nonsense out of there... but I'm not even referencing that Hellbound abortion of canon. I am speaking of the less well known (but still somewhat well known amongst nerdy grognards) quartet of Doom novels penned by Brad Lineaweaver and Dafydd ab Hugh (a pseudonym for another author) where it is eventually established that the Doom invasion of Phobos and then Earth is actually formulated by a race of advanced aliens who decided to use Demonic imagery as the template for which to base their invasion off of, hence all of the demonic, undead, fiery and in some cases... Nazi imagery that populated early Doom video game canon.
But I get what your saying... so what if they are aliens... they're still dedicated murderhobo aliens. What's the ethical dilemma of slaughtering them. It's like slaughtering Tyranids… or Zerg or Robocallers for Collection Agencies.
But the novels (in their eventual descent into an absolutely divergent storyline almost wholly divergent of Doom, particularly the
fourth novel... the two main characters
have their personalities copied/cloned into an extremely advanced computer simulation and during their adventures realize that they can influence the 'Demon' host to the point they can actually convert them from their previous murderous ambitions and instead embrace an alternate path (which at its distillation seems to advocate more free thought and being less beholding to ripping and tearing everything non-demon). They manage to convert Imps, Mancubus, Cacodemons (tricky since whenever they opened their mouths they spit out fireballs) and a plethora of zombies. Notably I don't think any Revenants (or Demons or Hell Knight and their derivatives were open to alternative points of view). So clearly... at least in the simulated environment based on the novels setting, there was a capacity or potential for good.
What if... however unlikely, that was true here as well.