"and it die": at the hands of Heaven. "or be broken": by an animal. "or be seized": by robbers. I might think "or be broken," "or be seized," (that he is not liable) whether or not he could rescue it; it is, therefore, written "and it die." Just as death is characterized by insusceptibility to rescue, so, (only) in all such instances he is not liable. These are the words of R. Eliezer.
What If the Guardian Could Have Rescued the Animal
Mekhilta Tractate Nezikin 16:3