Often, the most important things are lost in the crash of events. The tumultuous overthrow of the Warchief, Garrosh Hellscream, obscures events that occur elsewhere and the implications of those events. This is natural - Orgrimmar's siege was a pivotal moment in the history of Azeroth and its resolution changed the political landscape of the Horde and established the Alliance's willingness to come together. An untested Warchief now must contend with a Horde full of fractious leaders and the roar of the Lion is once again heard over Azeroth. These events, the culmination of a year spent exploring a new land, are not surprisingly dominant in our minds.
But in the end it is in Pandaria that the truth is revealed. The world has changed. A profound alteration to a land locked away for ten thousand years, imprisoned by pride. Events were set in motion by our discovery of the land behind the mists, but their final denouement was not on the floor of Garrosh Hellscream's bastion beneath the streets of Orgrimmar, but rather in the Vale he casually destroyed to fuel his ambitions.
The Truth So Long Concealed
Upon Hellscream's defeat, the Heart of Y'Shaarj was no more - the Warchief drained it of every scrap of power the relic of the Old God had pilfered from the waters of the Vale in his stand against those that sought to bring him to justice. While Thrall himself utterly failed in his attempt to bring Hellscream down, others stepped forward and faced the might of Hellscream's loyal Kor'kron as well as the Warchief himself. In the end, Hellscream fell, and the Heart was no more.
While the leaders of Azeroth's people debated their next move, it was Lorewalker Cho who noted the remains of the Heart. And it was Lorewalker Cho who comprehended what it meant - that for the first time in untold thousands of years, even the many centuries before the mists came, Pandaria was forever free of the threat of Y'Shaarj's dark legacy. The undying dead god would no longer lurk, a dreadful secret, a dark heart of Pandaria itself. Y'Shaarj died long ago, true, but its threat did not diminish - indeed, in many ways, the last breath of the dying god had tainted Pandaria in a way that could not be removed from the land. The seven Sha, born at the instant of Y'Shaarj's 'death', could never be destroyed permanently so long as the hearts of mortals remained capable of anger, fear, doubt, violence, pride, hate and despair. They would spawn legions of lesser manifestations, and no matter what was done they could never truly be removed from the land.
Shaohao, the Last Emperor of Pandaria, did his best to remove their insidious presence from himself, and buried each in turn within the land of Pandaria itself, save only Pride. That last, most terrible of the Sha became the sheltering mists that sealed the land away from the horrors of the Sundering, preserving it just as the amber of the Dread Wastes preserves the Klaxxi paragons.
In the end, it meant a truly amazing thing.
The Sha, the eternally returning, always present menace that has threatened Pandaria for thousands upon thousands of years - the menaces that Shaohao himself only managed to seal within Pandaria - these dreadful manifestations of the negative emotions of those who walk upon Pandaria are gone. They have not been pushed back to return again. No longer does the continent need bind itself, forever repressing all emotions that could empower them. They have lost. Whether this means they're gone or that simply that without the Heart they can't reform is an open question, but considering that prior to Garrosh's fall all the Sha primes had been found and dealt with, up to and including Pride itself, defeated even as it sat and fed upon the hubris of the Warchief in the chamber where the Heart had once been imprisoned, it seems likely that the Sha can menace Pandaria no more.
This is a seismic shift in Pandaria's culture. Institutions like the Shado-Pan, who once stood guard over Pandaria, vigilant for any sign of Sha corruption now no longer need do so. The Shado-Pan were never purely about the Sha - in the absence of an Imperial Army they defended Pandaria from the Yaungol and Mantid encroaching on the Serpent's Spine - but their primary duty and genesis was in the threat of the Sha, and that threat has been dealt with. What the Emperor could only imprison, the outsider heroes have destroyed, and with the Heart no more there is no more of Y'Shaarj's taint left to recall the Sha again. In strange aeons like these, even the Sha may die.
This is not the only massive change to Pandaria, however. What of the mantid?
Following the events of the siege, we now have seen the loss of the great paragons who defined and protected mantid culture. The Klaxxi still exist - neither Klaxxi'va Vor nor other survivors of the council (those that managed to survive the fallen Empress Shek'zeer's destruction of most of their fellows) were found in Orgrimmar. Only the Paragons traveled to the Heart of Y'Shaarj, potentially because the council had the egg clutch of the future Empress to concern themselves with. But with the Heart destroyed, and the Paragons dead, what will the future hold for the mantid? The Klaxxi are reduced to a bare few, the last Empress dead before the next Empress could rise to challenge and consume her - their culture, so long preserved, has lost those that maintain and shape it and its very secret reason for being. The mantid are worshippers of a god who has finally, definitively been eradicated - nothing of Y'Shaarj exists, not even his dread final breath that brought in its wake madness and corruption even to the mantid that worshipped it. The Sha of Fear nearly destroyed the mantid people as it pushed Shek'zeer into paranoia. But even that was understandable to the Klaxxi, and the mantid - not only were the Sha only the merest whispers of the dead god, his last breath, but the old gods themselves were gods one worshipped out of fear anyway.
One didn't love Y'Shaarj, one desperately sought to placate it. Nevertheless, there is not even that left to the mantid now. What will they do? What will their Empress, when she comes of age, do to restore her people? Much of the Dread Wastes was destroyed by Sha corruption - several of the Kypari trees are dying, and with them the amber that is so central to their existence. Their old god is no more - not even the Heart remains. But there are other old gods - both C'thun and Yogg-Saron, despite their deaths at mortal hands, can still send whispers to followers (Cho'gall, for instance, heard C'thun whispering to him even as he died in the Bastion of Twilight, several years after C'thun's supposed death in Ahn'Qiraj) - and beyond that, even the whispers of Y'Shaarj hinted at dread Nyalotha (a city? another old god? both?) and we know N'Zoth has yet to reveal itself. Will Shek'zeer's replacement seek out an old god to follow? Unite the mantid with their qiraji and nerubian cousins?
The future is unwritten. For Pandaria, for the first time in over ten thousand years, it is not even knowable. What the destruction of Y'Shaarj's heart means for Pandaria is simple - a return to being a living part of the world.
While you don't need to have played the previous Warcraft games to enjoy World of Warcraft, a little history goes a long way toward making the game a lot more fun. Dig into even more of the lore and history behind the World of Warcraft in WoW Insider's Guide to Warcraft Lore.