At the end of the Siege of Orgrimmar the heroes of the story will have defeated Garrosh, and stopped his plans to use Sha powers to rule Azeroth. That is the expected outcome of the patch content. There is also some question on who the new Warchief of the Horde will be. I won’t spoil that for you.
I will spoil part of the story, as it is a part which I dislike. You have been warned if you read on.