Not Warhammer Fantasy again, plsAye. There are theories that Warcraft's universe is cyclic, in one form or another.
It's only natural; the Light and Shadow are waging a war over it; and if the naaru are anything to go by, then it's quite possible that when one side wins, the losing side can bounce right back (naaru, upon death, turn into void entities... strange that. A Holy being completely turns into a Void being).
Il'gynoth even hints at prophecies and known things in his Emerald Nightmare encounter:
"Your coming was foretold in the rings. The long circle is nearly complete."
Rings could be a pun; he is literally a tree in this encounter. But the long circle? Circles don't have a begining or an end; they are eternal. We could be on a constantly overlapping circle, in which the 2 cosmic forces are playing tug-of-war over us.