I've said this before so I'll just repost this here as it it very appropriate
Our Timeline's Histoy
The Tomb of Sargeras houses the corpse of the slain Avatar of Sargeras, Aegywnn the Guardian of Tirsfal was reported to have slain. The spirit of Sargeras survived in Aegywn and was passed down to Medivh from birth along with all the powers of a Guardian. Medivh would later seek to explore the darker nature of his power through the twisting nether and later find Gul'dan telepathically. Gul'dan agreed to bring his Fel Horde to Azeroth in return he would be given the location of the Tomb of Sargeras. Something or someone found Gul'dan in that tomb that left only a glowing green skull of one of the most powerful warlocks of all time. Arthas informs Illidan of the location of the Skull of Gul'dan which he obtains. Its knowledge also leads him to the Tomb. It too is lost below the waves only accessible to the Naga (future patch maybe.) The Eye of Sargeras taken from the temple was strong enough to destroy Icecrown from below moving Arthas to counter Illidan and drive him from Azeroth. Illidan and Vashj are also killed in the events leading to the Black Temple betrayal by Akama. The Tomb's location slips out of all recorded knowledge.
The Titan presence on Azeroth falls silent. Messages to the Pantheon are cut off. Titan Wardens that feared no Old God now dread a dark presence from below. The Tomb of Sargeras might be the Darkness that Ra'den warned us about. It also could be the reason why the last command the Black Prince absorbed through the Heart of the Thunder King (Ra-den's core) was to "REBUILD THE FINAL TITAN" Sargeras has found a way to make the robotic titan automatons below Azeroth forget their original duties and rebuild his form.
In out timeline Medivh was killed by Garona and Khadgar with an enchanted, however these new events would prevent his activities from ever exposing his evil to Lothar. The Gul'dan in our timeline was given this information by Medivh but he never lived to tell anyone else about it. Illidan only learned of it after he possessed the Skull of Gul'dan and we killed him before ever thinking to ask.
If we don't find out where Sargeras is hidden he could come he could Break out of the Ground all "Lavos" style and instantly one shot Azeroth. The only one with that knowledge is Medivh. If we could get to him before Sargeras completely took over his spirit we could possibly get the leader of the Burning Legion out in the open in our world as well before the Final Invasion.