Or so we thought the things would go. We knew the new Warchief is on his way, biding his time as the adventurers ever vanderlust headed for Siege of Orgrimmar. Where they would aid the combined but ever divided might of the Alliance and the Horde. I expected Garrosh to die, but for now let us focus on his successor, Chieftain of the Darkspear Trolls, Vol'jin.
Vol'jin is patient. Patient and cunning. He could not go against Garrosh until his life was endangered. To go against warchief just because you disagree with him is clear suicide. We have seen that with Thrall. I don't recall the details any more, but essentially an orc called for attack on Theramore. Thrall crushed him on the spot. Nobody ever again suggested attacking Theramore in Thrall's presence. Thrall said no killing women and children. A band of orcs killed women and children. Thrall had them executed. This is the institution of Warchief. He is the supreme judge and commander.
Orcs were not really satisfied with Thrall ever since he found a place for them under the scorching sun of Durotar, yet there was no open rebellion against him. Because Thrall allowed them to disagree with him. But he did not allow anyone to go against his explicit orders. This is where Garrosh made a mistake. Garrosh took every critique on his account as usurpation. Something he would not allow. The institution of Warchief is much closer to a Roman Consul than a normal king. Garrosh acted like a king. He demanded obedience and servitude from everyone. He did not tolerate any disagreements. Not a king, a tyrant.
Thrall on other hand, had a much more consular approach to his position. He knew the other leaders of the Horde are his equals, not his subjects. And he treated them this way as well. He took advice from them, listened to them and acted according with their thoughts on the matter. This is seen when first Forsaken joined the Horde, and later when Sylvanas essentially took Blood Elves under her wing to join the Horde.
Vol'jin has Thrall's approach to politics. Yet he does not care for Alliance as half as much as Thrall did. His main objective is not a peace with Alliance. His main concern is not about Alliance. Vol'Jin's main concern is well being of the whole Horde. If that does not sit well with the Alliance, then so be it. For all that Vo'jin cares Alliance can go and sulk in the corner.
This, will probably lead to conflicts in future. As much as Alliance would like it, Vol'jin is not going to give up on the territory that Garrosh conquered in his short time as Warchief just because they helped him to get the throne. No matter the action's that lead to the fall of Garrosh, the lands he conquered for the Horde still remain vital for the survival of the Horde.
As for Sylvanas and her rampant disregard for rules and orders, there is practically nothing that can be done. With Garrosh gone, Sylvanas has once again full control over her territory. With no loyal soldiers of warchief to breathe down her neck, and look under her fingers she is free to do whatever she pleases. In this case, more war.
One of the main concerns Alliance has is Sylvanas. She is using plague weapons, raising dead, fighting total war. And unlike with other enemies, fighting a total war against the Forsaken is a lost cause. The more men you throw against them, larger, greater and stronger their army becomes.
Sylvanas is like black queen on a field of chess just before she has the white king in check. You know you must save the king but no matter what you do, that black queen will still eat couple of your figures.