The Death of Arthas
Here is a recap of how he dies for those who do not want to witness the videos of it. You basically walked into Icecrown Citadel and kill all of his strongest allies. Then you arrive to the frozen throne where Arthas freezes Tirion and describes his grand scheme. He would test you against his finest soldiers and should you succeed then he would capture your souls himself and turn you to his side.
So you battle Arthas and finally defeat him, at about 10%. He then kills the entire raid and channels some kind of undead resurrection spell. Tirion calls upon the Holy Light to break the ice heâ€™s encased in and destroys Frostmourne. This releases King Menethil who resurrects all of the players who then kill the Lich King and bring about the end of his reign.
Frostmourne is shattered.
Sitting on the Frozen Throne is Bolvar Fordragon who is now burning eternally. Tirion takes and places the helmet on his head and crowns him the new Lich King, since as we discussed before there must always be a Lich King. That concludes the main storyline of the expansion and ends the terror of the Lich King.
What Does This Mean Going Forward?
So now, we ask, what does this mean going into Cataclysm? Well it means that the undead will still exist, but there will no longer be a menacing force causing the plagues and the untold amounts of death. They will just be walking corpses, hopefully without any organization or some ultimate guy resurrecting as many corpses as he can get his hands on. Bolvar will also get to stay pretty chilly at the Frozen Throne.
There were many races in Northrend. The Vyrkul, for instance, are now without a king, a god, or their death god (Arthas). Where is their place in the world? A long forgotten enemy model or perhaps theyâ€™ll have a nice warm home in Desolace once itâ€™s rebuilt.
The Tuskarr are unable to leave Northrend because there is a quest that states they will die should they go to a warm climate. So I assume we wonâ€™t be seeing anymore of them after all is said and done.
The Taunka and the Earthen Dwarves will obviously join up with the Horde and Alliances in Cataclysm. I imagine their models will be used for various quest givers, but I doubt theyâ€™ll have any dedicated cities since those seem reserved for playable races or for the new races in an expansion. We didnâ€™t get any Ethereum cities in WotLK.
In the end I think that a lot of the events in WotLK will be soon escape the minds of players as return to the original Orcs vs. Humans storyline. Perhaps, somehow, weâ€™ll still be able to stay in touch with all of the new friends weâ€™ve made in Northrend now that the Lich King is dead and peace can return.
What would happen if Arthas wins? Letâ€™s say that you, the adventurers, join him in death and become the leaders of his army. The answer is a curious one. If we assume that there is no resistance than we can only assume that Arthas turns the entire world of Azeroth undead and probably invades Outland as well doing the same. With that, heâ€™d have a massive army and a â€œperfect worldâ€ of people who would not suffer death because they are immortal.
Iâ€™d imagine then it boils down to two things. First off is the Old Gods and Deathwing. Would an entire world of undead be enough to stop him? I wouldnâ€™t be able to answer that question without knowing how powerful Deathwing truly is, but I imagine that heâ€™d be able to hold his own. Assuming he wins then itâ€™d boil down to The Burning Legion.
Arthas would obviously lust to conquer more and would probably eventually meet his demise at the hands of the Burning Legion. While he can turn armies against themselves, his power comes from them, and if we learn anything itâ€™s that you canâ€™t defeat someone with their own power. Unless itâ€™s a channeled spell of course.