I always pondered on the fact that through all the hardwork at the end of The Wrath of the Lich King, if you go down into technical terms, we never slayed the Lich King, we merely slayed Arthas. Knowing that fact, Bolvar Fordragon never gave into the Lich King's will and is now jailer of the damned - imprisoning the Lich King within the Frozen Throne once more and containing the threat of the Scourge, brings a lot to mind.
What do you think Blizzard will ever do with that story, if they ever do. Will they bring him back at some point, even just to find out more? Thoughts...?