I was thinking about the Timeless Isle, and what sort of effect it would have on a death knight. The overall theme you get while talking with the NPCs there is that nobody can tell how much time has passed between events.
I was thinking that a death knight might remain in whatever state they were in when they arrived on the Timeless Isle. That is, if they got there and stopped killing things, they’d not go insane from their need to inflict pain. However, killing things while on the timeless isle, does not bring them any release, either. So a death knight that was on edge when they got there would remain on edge until he left, regardless of what he killed.