Xu Rufeng was confident that he had done quite well. When he took action against Tang Ye, if he could defeat him, he would have killed Tang Ye. If he lost, just as now, he would pay a sufficient price. Even though he hadn't died, he had ruined half of his face. As a conspirator, having made such a sacrifice, what more could he ask for?
However, the requirement of Poison Snake was that if he lost, then he should die. Death was the most reliable method of arrangement. Firstly, if he died, no clues could be investigated. Secondly, his death would further incite the rage of the martial artists against Tang Ye, thus achieving their goal.