Newbie but on my way..

Your consultant and other members of your medical team have had the benefit of seeing your scans, which we haven't. The surgeon is obliged to operate in a way that preserves tyour life and eradicates the cancer. Presumably, they are concerned enough about the siting of your tumour to believe that it isn't a good idea to leave that nerve bundle. To leave a nerve bundle intact could be likened to leaving the outer skin of the prostate - imagine that a cobweb is fixed to the outside of an apple and they are trying to remove the apple without disturbing the cobweb. That means leaving some of the apple-skin but as little of the apple white as possible.  

If leaving a nerve bundle behind means that there is a chance of any cancer being left behind, a responsible surgeon simply won't do it.

The science says that only having one set of nerves reduces the chance of erectile recovery. But not as straightforward as you might imagine - there are men who have full nerve-sparing but never regain erections, even with chemical / mechanical help. There are men who have non-nerve sparing and somehow recover. Men with some nerves may be impotent for the rest of their lives, may manage fine with help or may recover fully. See my 'one wife's story of ED' for John's experience - one bundle saved, lots of angst but full recovery of natural erections about 4 years post-op. Unfortunately, no cure though - the op didn't get it all so salvage treatment 2 years later and now holding our breath in case it has come back again. Possible reason for this? They left the nerve bundle on the side they believed was unaffected but once it was in a petrie dish it turned out there was far more cancer on the 'nerves saved' side than the 'nerves removed' side. 

Gleason 3+4 organ confined... pT2c Nx with all the margins negative.

Sildenafil on its way... :-)