If a nerve has been damaged enough or has died then yes, it's permanent. Nerves can't be "repaired" or regenerated, at least as of now. I've been dealing with idiopathic poly neuropathy in my feet for over 10 years, and it's not going to get any better, ever. Three neurologists, 2 neurosurgeons, and my GP have all told me the same thing, once a nerve has been damaged or has died that's it, there's nothing they can do for you except to try to control the pain.