The war ended with the death of Voldemort. His legions found themselves on their own again. Most were thankful, some still believed the same things and found themselves wanting to continue their fight for their belief. Instead of death to those not part of their world view, as they found the populous really did look down on that sort of thing, the followers simply returned to their lives from before the events at the World Cup and plotted their eventual success through more socially acceptable means. And for the most part, the British wizarding world allowed it.