There is a term I helped coin a couple years ago, the Wightocolypse, where wights really DO take over the world. It basically stems from ground zero of a Snowcasting Flashfrost Fell Draining Locate City bomb. Anything with 1 HD or less becomes a wight in ~12-24 hours, and anything with more HD than that will be slain the following night by thousands, or hundreds of thousands of wights, becoming wights themselves. Basically, the D&D equivalent of 28 days later. Its very very VERY grimdark.
