If you go ahead and purchase this baby, not only are you supporting a mill, but in turn another baby will just take this one's place and it's an endless cycle. If they won't refund your deposit, I'd consider it a lesson learned. You DO NOT want the heartache of a possibly sick pup that could cost you thousands. I know you think you love this puppy already, but honestly, a lot of the time the pictures you're seeing of an adorable little pup isn't even THE pup you'd get. The mills are known for this, they show you pictures of a healthy-looking pretty little puppy and what arrives on the plane is a different dog.
Please consider checking out
Yorkshire Terrier Club of America, they have a breeder contact page. You will have the best chances of finding a healthy, good quality pup from a breeder there. The breeders also stand by their pups in many ways that a miller won't.
Good luck!!!