No, C'Thun has not been killed yet
, but there are already rumors floating around as to what he might drop
. Sure, there's no proof of any of this, but news of this nature seems to inevitably leak early - from Nefarian's loot tables to every set of patch notes. Casters will immediately be drawn to a new legendary item - a trinket dubbed The Piercing Eye of the Abyss. It gives an underwhelming bonus of 2% spell crit but also has the following interesting effect...Upon death, you have a chance to be possessed by the spirit of the Old God for 20 seconds. While possessed you cannot be attacked or targeted by any spells or effects and your damage spells deal bonus Shadow damage. When the effect ends, you die.
While certainly interesting, I'm not entirely sure what to make of this item, or any other item that requires your death as a pre-requisite for usefulness.