Speak with Loramus Thalipedes in Azshara.
The triad is protected by Razelikh.
In exchange for their servitude, Razelikh granted each of them nearly unlimited power within the Blasted Lands. The amulet pieces are each attuned to the lifeforce of their owner, granting them immortality. As long as they remain within the Blasted Lands, they cannot be slain, their life spans extended until the end of days.
There is one who may be able to assist you further, [player]. Travel to Azshara and find the demon hunter, Loramus Thalipedes. Search the islands.