Having already had my treatment the answer to this question is only of academic interest but I'm sure will help others, I don't know the answer and hoping someone does.
I know there is no need for an erection to have an orgasm. My penis is not very reliable on erections, but I still have amazing orgasms.
I know that ejaculation isn't necessary for orgasm, as mine were dry post treatment, but do seem to be becoming wetter. I still get the feeling the prostate is pumping whether dry or wet.
I am going to assume an orgasm happens in the brain, probably in the brain stem, as I assume orgasm are fundamental to life.
My guess is three sets of nerves are involved in sex:
1. brain to penis "get an erection"
2. (Tip of) penis to brain "this feels nice, I must be in the right place"
3. a. Brain to penis "shoot your load, and have fun whilst you're there".
b. Brain to face "do the really silly expression (and hope she has her eyes closed)"
c. Brain to toes "curl"
With none nerve sparing I know the the first set of signals "get an erection" are lost.
Do the second signals from penis to brain get through?
Does an orgasm happen in brain?
Do signals 3a happen? Is there a pleasurable sensation in penis during orgasm?
3b, Do I still get to do the funny face?
3c Do toes still curl?
I think knowing the answer to these questions would help people make an informed choice.