From what I have seen of people who have used hard drugs for a considerable amount of time I would say the answer is "No". Sorry to be pessimistic, but the brain just is not the same and the person's actions, words and patterns of behavior are never normal again even long after they have detoxed and stopped using the drugs. I have seen many people like this and they say and do strange things in small ways - by this I mean - you would have to be around them for quite awhile to notice certain patterns or should I say instances of slurred words, silence when asked a question, day-dreaming, etc.
The problem with hard drugs is that most of them directly effect your brain. Things like Xtasy and Meth effect pleasure sensors and glands in your brain, causing them to prematurely burn out. Problems with the brain do not heal and do not go away. Once brain cells and glands are done, they do not recover. So the short answer is no, any damage from hard drugs is not reversible, because if you make it far enough to have damage, then you have gone to long already.