Something may be a little off with this story, so be careful responding to it.
I worked with bomb dogs and the Marines were told to NOT get attached to their dogs as they will never get to keep them and could very easily be given to another soldier to work at any time.In fact half way thru Marine training several dogs were swapped around just to make it clear that the dogs are not theirs to keep.
If hurt when the dog recovered he was redeployed with the next marine in line. The dogs needed to stay where they would work for anyone handling them and the military needed to get as much value out of their investment as possible. There are thousands of dollars tied up in a dog by the time it is trained. Their training is carried out by numerous trainers so the dogs work for anyone and their work ethic is totally independent of bonding. Also they did not want the Marines to "protect" their dogs and keep them from working, or put themselves in danger to protect their dog.
How can you promise a handler they can keep their dog when its been in several soldiers hands.
Its more manageable to tell them all they will NOT get the dog.
I do like the idea of having retired dogs going to injured marines-- just not guaranteeing it will be the one they worked with.
I have a gut feeling that dog was redeployed and they don't want to tell him that. It may have gotten injured again. Being a bomb dog with remote detonators around is risky. They would rather get rid of a single dog than a bunch of marines, they are extremely effective.