Zhou Tian's actions lasted for over half a day, killing nearly a thousand NPCs and players in almost a day. Although 99% of them were NPCs, Zhou Tian still gained massive merits from this mission.
After gaining merits, Zhou Tian chose to retreat without hesitation when the NPCs realized what was happening and prepared to come out of the stronghold to confront him. As a result, the NPC army barely had time to catch a glimpse of Zhou Tian before they noticed the lower-level monsters that had been present outside their outpost were miraculously gone.
Honestly, considering the circumstances then, the NPCs could have easily retrieved the territories that Zhou Tian had newly acquired. However, just as Zhou Tian had figured, the NPCs were utterly unprepared to take over those territories. Knowing the potential consequences of their actions, the NPCs could only reluctantly withdraw their troops when they couldn't locate Zhou Tian.