Lol! His hair will grow back unless he's having some type of issue internally/alopecia. Maybe it's the groomers' preference not to cut hair until 6 months, but I can't think of any reason why they wouldn't. His new hair growth won't be damaged and he won't have bald spots from a bad cut job
. Hair is already dead once you see it come from his skin/scalp. The "root" with the little white bulb attached is the living part of hair and as long as it wasn't damaged he'll be fine. Personally, I would look into finding a new groomer if they don't know the basics of hair growth and reasons it won't.