What is the ruling when a permissible animal is struck, falls into water, and dies, with the cause of death being unknown (strike or water)?

Primary text

If an edible animal is struck and subsequently dies in water without certainty if death resulted from the injury or the water, the water remains on its original state of purity. The animal remains prohibited (on its original state of prohibition), unless the injury was lethal, in which case the animal is permissible because the presumption is that death resulted from the injury, and the water is pure unless blood falls into it.