But again, you've got people who improve from severe or very severe to moderate or mild, like the prominent German advocate Martin (pausedME is his username in various places i think) you've got people like me who improve back to the top end of severe from borderline very severe and highly sensitive to all stimuli. You have many case studies and reports of severe people who are much better after x or y drug. So even if those drugs don't work, those people really improved. If severe symptoms were caused by irreversible neuron loss that wouldn't happen.
I suppose until we know the mechinism enough for effective treatments to be developed there is always a possibility of the whole permanent untreatable thing, but I'm not sure I buy it.