With the fact that Kel'Thuzad's phylactery was never Destroyed during the fall of Kel'Thuzad quest there's a perfect opportunity for the turtle wow team to create a unique Quest chain that would revolve around the cult of the dammed attempting to Return their master to corporal form
The Quest chain would lead players to a final Battle against the lich-lord's servants resulting in Kel'Thuzad's phylactery being permanently Destroyed once and for all
The Quest chain would start with players helping the Argent dawn investigate what happened to Kel'Thuzad's phylactery as they never received it. Players are in turn lead to father Inigo Montoy who reveals that he is a member of the cult of the dammed and that Kel'Thuzad will soon return before attacking the players who kill the treacherous Priest
With this knowledge the Argent Dawn send players to raid scourge strongholds In order to gain information on the location of Kel'Thuzad's Return
Eventually the Argent dawn discover the location of the dark ritual and send players to Destroy the lich's phylactery and prevent Kel'Thuzad from regaining corporal form
This Quest chain would introduce a brand new raid known as the Scolomance crypts which lie far beneath the Scolomance. These shadowy tunnels are where the cult of the dammed are attempting to restore Kel'Thuzad to corporal form