No it is not true. In fact the peripheral nerves can regenerate.

What is true is that a certain form of neuropathy called reflex sympathetic dystrophy has a poor prognosis, but it is not that common.

If a toxin or poison or whatever is continually present, and constantly harming the nerves, and is not removed then yes, poor outlook for that.

Some nerves may be permanently damaged, but that is usually done surgically. For example I had surgery to my left instep for a vascular tumor when I was 12. ( I had over 30 stitches) The area was numb for about 20 years, but it is no longer numb today. They all grew back.

If you sever the spinal cord, it does not regenerate, those nerves are CNS nerves. Medical science is still looking for ways to repair that, to help quadraplegics and paraplegics.

When nerves die because of a genetic hereditary disorder, they do not come back either.

This is why I suggested you stop reading the net... you can find all sorts of confusing, and perhaps inaccurate scary things on the net.