It's not a glassball. It's what will happen. The Horde are Shattered that they will need the help of the Alliance to clear that mess, the Alliance is more united than ever, Garrosh has challenged every Neutral Faction in the game so much that they already started going Alliance (Kirin Tor anyone) and the Horde's reputation with the rest of Azeroth is shattered. It's natural that they will be in a dangerous position. Of course they won't eliminate them. They will probably spare them but with some heavy terms of surrender. After all they will need their help for the Burning Legion after.
After all The Alliance exists because of the Horde (stated in the quest for The Black Morass) and not the opposite.