Hi Pat
IMO, its not a question of failure if you end up on insulin. One should use the least amount of medicine that most effectively controls your BG levels given your disease, lifestyle and diet.
If it is insulin or metformin that's should be not the issue.
In my experience after 1 1/2 years on insulin with very tight control both with lifestyle diet and insulin my foot neropathy is 90 to 95% cleared up and my readers went from 2.25 to 1.
All neropathy are not the same but my belief is that if you can get your BS down to low normal levels with minimal post meal spikes you can reverse and prevent some nerve damage but it takes years.
Insulin and strict diet and exercise in my opinion is the only way for many to have tight control.
I'd read Dr. Bernstein's book Diabetes Solution to gain a better understanding of just what this requires