A question I have been researching as well. My son fractured his neck over the Labor Day weekend (C-5 incomplete burst fracture) and is now a 'quad'.
There seems to be some indication, in at least Spinal Cord Injury circles, that new nerve growth is possble to replace damaged SCI nerves.
It is a very slow (many months or years) and tedious process and involves dedicated therapy (with repeated patterns) to do so. Dr. McDonald seems to think that even if there is no function, repeated therapy will 'awaken' certain functions and regrowth may or may nor occur, but new growth can.
It is similar to the larger branches of a tree that has met an obstacle, growing new smaller branches out of the sides of the main branch and growing around the obstacle
(bad imagery, but I think you get the idea).

We, who have PN, haven't really had successful similar research- but I don't see why the same principles wouldn't apply to damaged nerves in the peripheral system.

The problem is that we cannot do the repeated therapy to 'awaken' very easily. Burning soles of feet, or pain in our legs- is not the same as trying to re-make damaged nerves that involve finger or leg movement.
But with the right type of medications & suppliments, I don't see why we can't try to make the nerves have optimum nutrients and give them the optimum platform so that they can either repair, or let alternate new pathways develop.
There has been some, but not a lot of research in repair of the peripheral system that has been fruitful. Most is concentrated on the central system/spinal column, & surgical implantation techniques involving reprogrammable virgin cellular material (stem cells) that can replace the damaged cells.
Peripheral cells are much smaller and not as easy to work with. But I think that they can be given the right atmosphere to repair and regrow. I think that this does happen, and is happening- in some cases of PN recovery, or at least partial recovery.