Originally Posted by
FLANOFETT
You are right! just found this:
After the death of the Lich King Arthas Menethil, Sylvanas ventured alone to the Frozen Throne. While irritated that she was not there to see him fall, Sylvanas took solace in knowing that the work she had begun in the lush forests of Quel'Thalas was at last complete: Arthas was dead. With her life's - and unlife's - goal sated, Sylvanas could think only of the bright fate that had awaited her before Arthas tore out her soul and prepared to hurl herself from the citadel onto the saronite spikes below, the only thing capable of destroying her completely. As she contemplated the end of her long journey, nine val'kyr encircled her, granting her visions of her past. Sylvanas ignored them, and hurled herself off the Frozen Throne.
Sylvanas saw vision of her peoples' future. Without her leadership, the bulk of the Forsaken were sacrificed by Garrosh Hellscream in a failed assault on Gilneas. At the Bulwark, Apothecary Lydon organizes a last, desperate counterattack against the invading Alliance forces. As the tide turned against them, the Forsaken threw themselves into raging fires rather than face the onslaught to come. As the vision ended, Sylvanas found herself floating in a dark void, where she knew only terror, cold, hopelessness, fear, and regret. She also ran into the ghost of Arthas and was surprised to find that all he was at this point was a frightened and lonely little boy. Looking at the man who had inflicted such torment, Sylvanas admitted that had her soul not been broken she may have actually felt pity for him despite what he had done to her. As she realized that this realm of anguish was to be her eternity, the val'kyr appeared to her again. Led by Annhylde the Caller, they offered the Dark Lady a pact: instead of allowing Sylvanas to reside eternally in this terrifying realm, Annhylde offered to take her place if she binds herself to the remaining val'kyr; a powerful vessel through which they can continue to exist as more than slaves, their fates intertwined. Sylvanas accepted the pact, and was returned to the realm of the living surrounded by the eight remaining val'kyr.
Sylvanas returned to Silverpine Forest, where Garrosh was leading the assault on Gilneas, and stated that the invasion would be carried out her way; Garrosh begrudgingly accepted, and Sylvanas ordered her fleet around to the southern coast to harass the villages and split Gilneas' defenders. Reflecting on what she had been through, Sylvanas realized that her people were no longer simply arrows in her quiver, but an important resource that would not be squandered.[15]
So I guess dark void means exactly that, the void