Zhao Hai didn't pay any attention to the injured demon. He believed that the demon was dead for sure. It was only because the demon's life force was too strong that he was able to move even after being attacked.
Zhao Hai's judgment was correct. The Fiend was indeed on the verge of death. However, The Fiend Race had always lived in the vile environment of the devil World. They had grown up in a massacre, so their vitality was extremely strong. Even when their injuries were treated with the most severe treatment, they would not die immediately. They would only die after a counterattack. This was the case for The Fiend Race.