Poor dog! I hope she doesn't go back to the original owner. He doesn't deserve to keep her after giving up on her so readily.
I hope he doesn't either. I can understand why he left the dog, I don't understand why he didn't go back for him.
If he left him for dead, that's it. He abandoned his dog.
Someone else picked him up and risked their lives for him and took him into a vet for care, so THOSE people should now be his new owner.