I'm sorry to hear your dog has hearing loss. I have an older dog who has lost most of her hearing, and it has created new challenges for us.
Hearing loss from loud noises is a problem with the military and working dogs, as well as hunting dogs. In addition, we see cases of hearing loss and/or equilibrium problems from ear infections and from reactions to medications or cleaners placed in the ears, or any dog exposed to chronic or sudden loud noise.
Hearing loss from noise is complicated and the return of hearing depends on a number of factors. However, the intensity and duration of the noise is important. Chronic exposure to loud noises with subsequent hearing loss carries a worse prognosis then a single loud noise. For example, a given noise for 2 hours causes the same damage as a noise twice as loud for 1 hour.
Sound intensity is measured in decibels. This is a logarithmic scale related to some reference as 0, usually defined as the normal hearing threshold for humans. Being logarithmic, going say from 60 dB to 70dB is twice as loud.
Here's some examples:
0 dB: a mosquito flying 3 m away
40 dB: bird singing
60 dB: lively discussion
70 dB: vacuum cleaner
95 dB: saw (at ear)
126 dB: Rock Music Live concert
140 dB: Rifle being fired at 1 m
There's is only a small a amount of literature available for dogs, but more in cats. In general, anything above 85 dB can cause hearing loss with long-term exposure. Short-term exposure can cause damage at 120 dB. To answer your questions, if it was a sudden loud noise, there is good hope for return of partial or most of the hearing within weeks to months. Chronic hearing loss may improve, but then again, it may not. It's interesting that your dog is a blue merle/pit bull - blue merles and pits can have color-related hearing partial and complete deafness. However, they are born with this condition - it wouldn't develop at a year of age.
The good news is that the ear drums should heal fine in several weeks. You should arrange a follow-up visit with your veterinarian for 2-4 weeks to monitor healing. In addition, you may want to inquire if your vet can refer you to a veterinarian who has a Video Endoscope, if your vet does not have one. It will enable the vet to monitor the healing much better, and to look for development of fluid in the middle ear, behind the ear drum.
You will only want to use approved products in the ear until it heals, so no cleaners or medications unless you have the green light from your doctor. No swimming, and if you have to give him a bath, place cotton balls in his ears to keep the water out during the bath,
In addition, your doctor may want to place your dog on an antibiotic that has good penetration to the middle/inner ear, if he/she hasn't done so already. (just as a prevention).
Hopefully his hearing will improve soon. If it stays diminished, then I recommend a dog whistle if he can hear it, and to look into training collars for hearing-impaired dogs. Luckily their other senses are so acute, most dogs with hearing loss do very well.