You have to look at the story from the perspective of the writer. Who is developing, what would be shocking, ect. I think Sylvanas is going to prove to be a great leader. Somewhere down the road, they'll recognize those qualities. Honestly, if she led the 'Horde' like she leads the Forsaken, then Alliance would be stomped out. Unfortunately, she is dead and void of compassion. Garrosh is an angrier less intelligent version of Sylvanas. He can get the job done and in some instances can learn humiliation, and I see him getting himself killed. In the end, it'll be in the name of the Horde, but I see him being killed by someone from the Alliance.

I'm actually hoping that Garrosh and Varian end up killing each other. The Horde decide to lead as a council of leaders (after inner-conflict of course), and the Alliance are led by by Anduin. Look at his story. They're making him ready to be this peace-seeking Ruler, but after witnessing the death of his Father, maybe that'll all change.

Will this all happen in MoP? I don't think so. They'll wait until after Warcraft 4, if it ever happens at all. I suspect that MoP will lead up to it.