Hmm, I seem to remember that is exactly what Kairozdormu was thinking when he brought Garrosh to Draenor. This unfortunately is exactly why we have this expansion... Without Alternate Gul'Dan... the Legion would have no one to open the portal on Azeroth.
But, This kind of thinking that. "Infinite" realities would be powerful enough to stop the legion, is why the "infinite" dragon flight exists. I suspect based on how they talk, they probably have witnessed many realities fall to demons, (or old gods? or both?). However, I feel like somehow our "prime" timeline is important, because the demons are very intent on getting at it. Specifically the World-Soul of Azeroth. (which maybe doesnt exist outside the prime timeline?) (Titans are singular beings I believe, there are not many Aman'Thuls... )
From the lore, it seems the Demons want to destroy Azeroth... because it is corrupted by the old gods. Sargeras wants to prevent its birth, because it will become some kind of All powerful Void God.
Its entirely likely the end of WoW will be the apocalypse... followed by a nearly endless battle against Azeroth, as it tries to end the universe. Probably inside it on its surface etc. It will probably become some combination of the old gods, Like all of them at once. Who knows. it would be pretty epic to think about.