Some manner of glitch occurs at the end of Halls of Reflection; when Arthas arrives and grabs Jaina, the Skybreaker arrives, but the final sequence where the ship fires and ends the encounter does not trigger, leaving the dungeon stuck with Arthas eternally choking the life out of Jaina.
Dying does not fix the bug. Leaving the dungeon for an extended time does not trigger a reset, and I even tried not DPSing Arthas during the encounter JIC that had anything to do with it.
The dungeon is just stuck until the player manually resets and loses that loot from the Escape From Arthas fight. I even tried just waiting for a really, really, really long time to see if the event would EVENTUALLY happen, but no.