Lu Xuan had never been the type who relied on fate. The Taichu Path's existence and Yan Han's plans to take him out meant that he had plans to counter such a menace for a long time now. He would've even gotten rid of it while it still had a chance to grow any larger.
Mr. Wang explained, "Mr. Lu, it is true that the Sanxian Sect does have a transportation formation leading towards the Blessed Enclave. After Liu Bowen severed the dragon's vein, however, it was rendered completely useless. We're only able to come here from the Blessed Enclave, and have no way of returning."
Liu Bowen severing the dragon's vein could've been considered the same as severing the bridge linking the worlds together. That was why the connection between the Blessed Enclave and the secular world was severed right away.
While the formation itself survived the ages, it was still rendered completely useless.