Azshara uses the energies at the bottom of the maelstorm to open a portal to legion. However, because players had stopped most of the damage in catalysm, the portal is not powerful enough to pass through. Azshara uses the portal to communicate with Sargeras.
Azshara and Sargeras need an artifact which was split in two pieces by aman'thul to gain the titan power of being able to create portals to any world.
First artifact lies on Azeroth. Azshara and her armies start an assault on the artifact. Horde and alliance must join forces to stop her.
Second artifact lies in Great Dark Beyond (gdb) in legion heartlands. However, the titans do not want sargeras to have this power. They assault the great dark beyond. However, titans powers are limited in the legion heartland so they use their powers to create a temporal rift from azeroth to the great dark beyond and ask alliance and horde for help. Both sides are already beat up because of the assault by Azshara. In Azeroth's time of need, Tirion Fordring calls upon an old friend and the lich king sends undead armies through the temporal rift to help fight the legion. Horde and alliance fight with support of lich king's armies in Great dark beyond.
Azshara and Kil'Jaedan are able to plan great attacks against horde and alliance by communicating through the portals. Lor'themar is killed by N'zoth who is Azshara's pawn. Heroes manage to kill N'zoth but Azshara escapes with the artifact. In the gdb, Lich king is killed after he helps kill Kill'jaedan. This is the first time heroes see sargeras who appears to kill lich king and takes the artifact and leaves. Azshara and Sargeras's plan has worked. Azshara and Sargeras combine the artifacts to create a portal to the titan city. Heroes help defend. Heroes learn new titan blessed paths of advancement. Jaina sacrifices herself to kill azshara and Thrall dies while trying to kill Sargeras. Two titans are also dead.
Sensing the titans as being weak, old gods launch an assault on azeroth. One alliance city and one horde city have been overtaken by old gods. Heroes must recreate the well of eternity gain access to old gods plains. titans help recreate well of eternity. Heroes must gather water from 4 places (streams of time, smouldering falls, river of elune and well of hatred). Two lie in titan worlds, one lies in legion world and one lies in ancient city of azgol'nerub under northrend.
Heroes gather the water and recreate well of eternity. Heroes assault the heart of old gods. Heroes win.
End Credits
----------------------------
Cut scene:
Old Gods have a vision of a child formed of evil and malice and hatred. a child formed by the joining of two of the most powerful evils. Azshara and Sargeras had a baby.
-----A little while later-----
World of Warcraft II
Mod-note: Took my freedom to make your title a little more approving and appealing. Considering no one knows how the game will end, as well as Blizzard's continues pokes on not planning a WoW2. Though I allow your view of discussion, but remember people, THIS IS A FAN MADE OPINION. -- Gehco