During the time Shan Liangyi was in the Post-mortem World, Gua Tianshi, being severely injured and near death, was unable to destroy the Teleportation Door that the opposing side had left in the real world.
Even if it could be destroyed, it wouldn't make any difference, because after Shan Liangyi's victory, a new Teleportation Door could be swiftly built in the Post-mortem World, and the outcome would remain unchanged. Keeping the Teleportation Door in place in the real world, in contrast, provides an opportunity to pinpoint the exact time that Shan Liangyi and Evangelical Institute Master Yan Mo return to the real world. Thus, Gua Tianshi kept himself hidden while using surveillance methods to watch for any changes in the Teleportation Door.
Then he witnessed Shan Liangyi's return.
