WoWDB

Lord Itharius <Ambassador of the Green Dragonflight> in Orgrimmar is the NPC to speak with if a Horde player wants to watch the death cinematic for Deathwing. Itharius can be found west of the portals (just look for Deathwing's chin fragment, then down and to the right). He will also announce the defeat of Deathwing whenever a raid group slays the boss.

Citizens of Orgrimmar, rejoice! Deathwing is no more! The Cataclysm is over! A band of valiant heroes lashed out at the Destroyer with deadly precision and overwhelming might, granting the Dragon Aspects the opportunity to sacrifice their powers into one final strike. The last remains of Deathwing now reside here in Orgrimmar to serve as a beacon of hope for the future!

  For Alliance players, look for Chromie in Stormwind.