Oh, I am so sorry. It's so awful when something like this happens, but the hair will grow back. Within a couple weeks, it will look better. Until then, how about some cute little T-shirts?
I am only half kidding when I say that because mine love clothes...seriously! If you are wanting your baby to wear clothes, this might be a good time to start and with the hair short, rubbing and tangling should be minimized.
How long it takes for the hair to reach the length it was before the cut depends on how fast the hair grows...Mia's hair grows many times faster than Brody's and they're both silky. Also, your puppy will be losing the puppy hair at some point as the adult hair starts coming in, and there can be matting. I am not trying to make light of the trauma of getting an awful cut you didn't ask for and didn't want, but this could turn out to be a blessing in disguise. In any case, don't worry...your baby is adorable and even an awful haircut cannot change that!
I do most everything for my babies myself, but when I take them to the groomer it is for a "mini trim" which includes bath, nails, face, ears, paws, sanitary, and anals...no cutting on the body. She has different pricing for a trim and a mini trim. I have an ABSOLUTELY GREAT groomer, though, who I absolutely believe would do exactly what I asked for and would tell me if I wanted something ridiculous...she even got online and pulled up Yorkie cuts and pointed out one she'd thought I'd like...and it was the same one I'd been looking at online!
Good luck...{{{hugs}}}