I do feel for you. Maybe you could have a heart to heart with your son. And suggest that you buy them a new yorkie. This way they start fresh too!
I think it is worth a try???
P.S. My Mom went through the same thing. My sister and her boyfreind moved to Hawaii. They only had the puppy for a couple of months and then my Mom babysat (approx. 7 months) until all her records and shots, etc were in order so that LuLu would be granted Direct Release at the airport in Honolulu. My Mom was very sad, but all in all, it all worked out. LuLu is still in the family, she is now a Hawaiian Blonde Babe (She is a 6lbs. Silky Terrier). My sister and her boyfirend take GREAT care of her.