Some of the hair loss may be irreversible. When a dog is shaved, the top coat may never grow back in normally. The hair may be thin or patchy for the rest of his life. But at the same time, the hair may grow back in just fine. It could go either way.
Don't misunderstand what I am about to say. Your roommate had absolutely no right to shave your dog. He/she was one hundred percent out of line, and the damage to your dog's coat may very well be irreversible. Your roommate should cough up the money to take him to a vet and/or groomer so that you can get a better prognosis. But were you doing a good job of cleaning up after your dog? Clearly, the two of you need to go your separate ways, because there is no way the two of you are going to be able to be peaceful, cordial roommates. But having been a roommate myself years ago, I know what it's like to live with someone who does not clean up after their pets. Our original agreement was no pets. My roommate begged and begged me to change my mind. I finally gave in, but made it very clear that this was HIS dog, one hundred percent HIS responsibility, and that he must clean up after the dog. He did not keep up his end of the bargain. Our house was completely covered in dog hair. I could not even sit down on my couch without being covered in dog hair and dog odor. The house was covered in puddles and piles, the dog destroyed blinds, chewed up the furniture, and by the time it was all said and done, the dog caused about a thousand dollars worth of damage to the house we were renting. When you live with someone who has a pet but does not regularly clean up after the pet and keep the home swept and vacuumed, it can become extremely irritating. I would have NEVER done anything to my roommates dog, but I can certainly understand the frustration. If you are unable to vacuum and sweep daily and clean up after your pet, you should probably opt to not have roommates. Again, your roommate was one hundred percent wrong. Absolutely no argument there. But always make sure you are being considerate of your roommates when you have pets. Your roommates should never have to clean up dog hair, puddles, piles, or anything else caused by a dog that does not belong to him/her. If the dog hair was being swept and vacuumed daily, it is unlikely the situation would have escalated to this point, unless your roommate is just a sicko who gets pleasure out of shaving other people's dogs.