Indeed, Zhou Tian was very strong, but as long as they defeated him before his upgrade and drove him out of their sphere of influence, Zhou Tian's threat would cease to exist.
An upgraded Zhou Tian would be a formidable enemy to those NPCs, Zhou Tian on the verge of upgrading was an enemy to them, and a Zhou Tian who failed to upgrade and became an Emperor-level boss would merely be a moderately strong prey to those NPCs.
Therefore, to avoid Zhou Tian's revenge, the best outcome would naturally be to strike him down before he had the chance to grow stronger. If they could accomplish that, no matter how much Zhou Tian resented them, once he lost his ability to retaliate, they believed he would be unable to harm them.
