Even if they truly couldn't recover the lost territory, those NPCs were confident in their abilities to rebuild a castle. Although such a choice would incur significant losses, those NPCs would still be able to make that decision if they were willing.
In contrast, if Zhou Tian managed to annihilate the approaching large army of NPCs intent on attacking him, it would signify that for nearly a decade, the NPCs would barely be able to recover, facing such a loss, even the NPC demigods would be unable to bear the responsibility.
Therefore, even if they lost this territory, those NPCs likely couldn't endure the consequences of losing the large army of NPCs. This reason was why Zhou Tian devised the current plan.