Haha poor little guy will have hair again soon! It might change color too. My LO was born with black hair, it fell out between 6 weeks and like 3 months. It came back in as a light brown, sandy blonde.
Like others have said, don't be surprised if it comes back a different color. I'd also like to add that it may not come back for a long time! Dylan was sir baldy until he was almost 2 after being born with a full head of dark hair.