If your cat shows any signs of an ear mite infestation, take him to your vet immediately. Vet Andrea Harvey advises...
(Q) I recently adopted a stray neutered male who's about seven years old. He arrived at my vets with a broken jaw and needed treatment for ear mites, but the latter were so severe that he now has no hearing and has very disfigured ears. We asked our vet if surgery would give Sammy some hearing but he thought this would be impossible. Do you think I should get a second opinion on this?
Vet Andrea Harvey advises: It is difficult for me to pass judgement on Sammy's ears without seeing them for myself, so your vet is in the best position to advise you about that.
It certainly would be very unusual for any cause of deafness to be curable by surgery. Surgery would be more appropriate if Sammy was, for example, suffering recurrent ear infections because of the disfiguration of his ears, or if he had any masses within the ears such as 'polyps', benign inflammatory masses which can grow inside the ears.
If your vet is worried about any of these possibilities he may want to discuss Sammy with a specialist dermatologist (skin specialist) or consider referring him to one. But if Sammy is otherwise comfortable this may not be required.
I can't say what the cause of the deafness is but it sounds unlikely that any surgery is going to be able to restore his hearing. Ask your vet whether he thinks any further treatment is required, and whether getting a specialist opinion would be beneficial. It sounds as if your vet has done absolutely everything he can.