Severed nerves do heal in the periphery. And they typically act up and hurt while doing so. People trying to severe their pain signals often find they grow back. It is not likely you have severed a nerve.

But it is possible you created scar tissue from injury which continues to compress a nerve. Or you created an infarct which destroyed blood supply to nerves. If the nerves' cell bodies have died, you may not get those back.

Many things do not show up on MRIs....you will just have to see with time what happens.

That part of the anatomy is very subject to damage. Often damage from hidden diabetes or impaired glucose tolerance will show up as erectile dysfunction long before blood glucose starts to become problematic.

It might be useful to seek psychological counseling for your healing period.

I am surprised you haven't mentioned Viagra ...or Cialis. Testing with this drug would tell you if you have blood flow problems. If you see improvements with drugs of this type, that would point to blood flow damage. Erection is determined by nitric oxide release in the walls of the blood vessels. It can also be helped in a slower way with l-arginine.