It became part of the main timeline when Kairoz traveled to it. If we lost there the Iron Horde or the Legion would have came through the dark portal to invade Azeroth. However it was set up to be a little bit of a failure. We didn't stop Gul'dan. And he helped the Legion come to Azeroth in the new expansion. They still could have have set it up with us being routed from Draenor but it would require two expansions worth of the same bad guys or likely a terrible story transition.