Modern hearing aids can amplify and filter sound quite effectively, but they can't correct distortions of the sound, so your word recognition score is very important. If you score less than 50% on a word recognition test, a hearing aid won't help, it will just make the distorted sounds louder. Scoring 75% WR would be better.
Your overall hearing level before treatment is a useful guide to the likelihood of retaining usable hearing after treatment. It seems that the higher your hearing level going in, the more likely you are to retain some afterwards. If you are below 50% before treatment, the chances of retaining some hearing after treatment (and six months later) are not as good. I think that is the experience for both surgery and radiation treatment, by the way.
So in your case, if your word recognition is low, then saving it wouldn't do you much good, and if your overall level is already below 50%, there isn't much chance of saving it anyway. Hence your doctor's summation, 'You don't have enough hearing to risk saving.' I would still consider radiation treatment as a way to avoid other risks, but I would agree that it makes sense to choose translab over middle fossa as a surgical method.
Steve