I guess I personally lean towards "Were on the verge of death, but after making terrible agreement of the black exaltation, were spared; remain alive, but slowly becoming more like death". They're undeniably alive, though, so redemption into a Solar doesn't violate one of the two biggest damned rules of the setting; an Abyssal may seem to rot like a corpse, and subsist on essence alone without need for breath or food or water, but his body remains alive and intact despite these changes, and upon redemption, he becomes whole as solar essence purges necrotic essence and restores original functionality.
Failing that, "Kept on the cusp of death by necrotic essence, existing between life and death", but with the understanding that they're too far gone; redemption results in your shard leaving, becoming a Solar, and you dying. This also maintains one of the Big Two Rules of Exalted, "No Resurrection".
On Infernal logic:
(4:22:38 PM) Nekomimi Maiden: So I did the only logical thing.
(4:22:49 PM) Nekomimi Maiden: I fell in love with the bad guy and twisted his spine into a pretzel