The main problem with this consept is really that many people expect a character to have a disability of a kind, especially made up ones. It has become kind of compulsary for writers to include such a character. They even do it on television sometimes. IT may cause a level of issue with people who have disabilitys, especially when characters are cured by medical means. (Which usually is quite impossible.)
There is a level I believe you can stop at as it gives the character death and that all important 'want' as I call it, the thing they desire most. But unless you get it from the point of view of an actual person who has experienced this don't bother, or if your going to have them 'magically' cured like R.J said before. Characters need a problem but it can't disappear just like that or get worse, like in real life because many people hate both. You need it to happen with some depth. But not in extremes like it's the only way to save the universe or something because it's normally the other way round. Actually I can't think of a good reason myself to get rid of a disability, the character shouldn't lose it in my opinion but get used to it, or recover to a point, something like that as it keeps the character that everyone growed use to.