I Hate This Guy
The Fiends had already locked down the region, with both Thaldorin and Tyroth present and prepared in case anything went wrong. According to their initial estimates, it would take a while for the Real Plane experts to realize that something was amiss.
The death of a Dao God was incredibly rare. On one hand, it made it especially difficult to kill them—or rather, it proved how difficult it was. But on the other, the other side wouldn't be prepared for such an event at all.
Usually, powerful cultivators would have some sort of memento in their Clan to mark whether they were alive or dead. However, not only was it very difficult for a Dao God to create one themselves due to their power, but it was also a bit of a taboo, at least in this world.