One thing that you have not mentioned is whether you have gotten a CT scan
of the abdomen and a bone scan. The MRI/CT will tell us whether the disease has spread out of the prostate
or not and the bone scan will tell us if it has spread to the bones.A chest x-ray should also have been done to rule out spread to the lungs. If the disease is confined to the prostate and has not spread anywhere then a removal of the prostate by a cancer surgeon is advisable as the chances of cure with this surgery near 90%. However, that will put an end to his sex life as you already know. If he is absolutely adamant not to undergo surgery, then the only option available is radiotherapy plus hormone therapy
. These have their own set of side effects and may decrease the libido. However, it will not make him irreversibly impotent. The downside is that the cure rates will fall and there is a chance that the disease may actually progress and spread to other organs. So, in a nutshell i will advise you to motivate him for the surgery else he runs the risk of putting an early end to his life. In case the disease has already spread to other organs, then the only option is hormone therapy.