Ah.. just to clerify the people who were wondering this (Brought up at M&G was answered) the Scourge still exists but no body knows. Bolvar <New Lich King> is rounding em up :P if someone wants to clerify it a little better be my guest.
The entire Scourge population of the world could not have relocated to Northrend, without anybody noticing. Granted, no-one will know about the new Lich King for the time being. I think certain lore characters will figure it out eventually, like Sylvanus perhaps, but for the moment the world believes there is no Lich King and the Undead still existing must be a mystery.
Whilst not 100% certain, I believe the world only knows that the Lich King is dead, but that the Scourge are still remaining without any sort of command. Or something. Again, not quite sure, but someone's gonna figure out that Scourge are still there.
Or they could just be mindless undead. We, as players, know of the existence of undead that are neither Scourge or Forsaken; couldn't the common person assume that any remaining dead are just independent, potentially freed of the Lich King's grasp?
Yeah, okay the lick king is dead, but since Bolvar is over there doesn't he have like.. control over himself and is calling them back? wouldn't they still be a problem if they were still left as they were???