Some guy asked the same question during the WoW lore panel, but the guys from Blizzard were like "Nope!" which is a really lame answer.
If Saurfang/Maraad/Velen step through the portal won't they meet themselves? How is it a "No"? Can someone please explain this to me? This is not a time travel issue (actions in the past affecting future) it's a straight forward issue of double characters which I don't get.