I had no nerves spared and I can tell you it's not so bad.
I have not tried Viagra and the like -- my understanding is that they don't work when nerves are not present. This doesn't rule them out later, when (if!) there is evidence that some nerve function has returned.
I find vacuum pump and injections do work well -- but both need practice and persistence to find a technique that works reliably. If hubby was getting good erections before surgery, I think the chances are good that one or both of those will work for him too.