I was thinking this. At the core of this current HvA conflict is land and resources. The orcs continued push into Ashenvale is technically what started the fourth war. Everything Garrosh has done has been for the Orcs to thrive in better land. If the orcs simply remain in Durotar, another Garrosh will eventually rise.
So, anyone think that Orgrimmar may be destroyed in the siege, and the Orcs are forced to relocate? Or maybe druids and shaman will band together post seige and make Durotar fertile (more likely imo)