one of many things i realised shortly subsequent to my Problem Sleuth reread is, believe it or not, that Rose Lalonde’s grimdarkness and Kanaya’s rainbow drinkerism might be closer parallels than what is currently understood.
of course, we can all tell that rainbow drinkers are undead. they’re vampires, and Kanaya awakens into one after being shot through the torso with a laser and very clearly being dead for a time. but nothing really yells ‘undead’ about the grimdark transformation upon first look.
however…

when the hired muscle’s brain is touched by the tendril of a dark god, his skin turns grey and his eyes wide and blank. the narration announces that he is now undead - and that his alignment is now indeterminate! which could certainly be similarly applied to Rose after her communion with the horrorterrors.
while it might seem a bit of a stretch to hark all the way back to Problem Sleuth for such a specific bit of lore, it can’t be ignored that rainbow drinkers are very obviously derived in nature from PS’ candy corn vampire, with an incredibly high fastness state described, of course, as vampire fastness. the vampire’s skin even stays #ffffff white despite the fact that even the frankenstein form has a different skin colour and the zombie’s skin grayness is even more obvious in this form, indicating that pure white skin is a trait associated with vampirism.
additionally, if we can infer from this that grimdarkness and rainbow drinkerism are similar states, then Rose’s quick death at the blade of Jack Noir’s sword could be a pretty valid indicator of the extent of rainbow drinker survivability; but of course, a vampire’s defense always lay in its ability to dodge attacks, anyway. its only weakness is a very fast attack.