One of the things I've most wanted to make clear in this series is that neither the Scourge nor the Forsaken have the monopoly on undeath now. The Scourge were joined by the will of the Lich King, and the Forsaken defined by their defection from the Scourge's ranks under Sylvanas Windrunner, but neither group created the state and neither has exclusive control over the creation of new undead. There are still vast numbers of Scourge in Northrend today, milling about under the control of the new Lich King, held in check but still a potential threat to the world. The Forsaken grow in numbers and might due to no small part to Sylvanas' deal with the val'kyr and her own experiments with the Plague of Undeath.
But both of these groups, for all their numbers, are not the only means to create more of those trapped between life and the sepulcher. The Risen (former Scarlet Crusaders from Stratholme and Tyr's Hand, now enslaved by Balnazzar), ancient and modern self-willed undead, and even those directly cursed by unfathomable forces (such as the continent of Kalimdor itself) have all existed over the years.
With the parting of the Mists of Pandaria, it would be easy to forget that the lands of Kalimdor and the Eastern Kingdoms will not be standing still. We know that both Scarlet Monastery, home of those remaining forces that did not make the trip to Northrend as part of the Scarlet Onslaught after the onslaught of Acherus, and Scholomance itself will see new developments, new stories. As we turn our attention away from these cold, chill places, the dead refuse to remain quiet.