I agree, the least he could have done was put the poor dog out of it’s misery. One shot to the head and it’s done, rather than leaving it up there to starve to death which is quite cruel.
In all fairness, I think he thought rescuer's would go get her -
When they reached the bottom, Ortolani said he had a friend call the sheriff's office, but deputies said they couldn't send a rescue crew for a dog.
Taking your dog on a dangerous mountain climbing trip is insane anyway. The guy has the common sense of an amoeba.