I think there are some things with our difficult child that just can't be fixed -- executive function type items come to mind immediately. His ADHD medication helps, but it by no means is a perfect answer. I always feel fortunate that his medication helped to the extent that it allows him to access learning of a lot of other skills.
He's had all types of other treatments for motor skill delays, auditory processing disorder, language therapy, social skills training, counseling, IEP, and probably some others that slip my mind at the moment.
Because of the abuse he experienced from birth until 5 yrs old, I'm not sure his trust and attachment issues won't adversely impact his adult relationships. Then there's the possibility of adoption issues. [After he was dismissed from therapy, his counselor almost guarantee us that these issues would pop up in his teen or early adult years.] So treatment? Yes, he's had it. But time will tell if it has a lasting effect.
Until he was probably 10 or 11, on paper he look like a walking disaster. But again we were fortunate enough that the therapies helped. If he were to be evaluated today, without the evaluator having extensive background info on difficult child, he wouldn't come close to being considered a child with Pervasive Developmental Disorder (PDD). But I know it is still there and always will be.
Then there are the days when I think absolutely nothing we've done has worked, but thankfully, those days are few and far between. (I remember well the reverse; the occasional "good day" we would have between +/-5 to 7 yrs old.)
And I dread his episodes, e.g., about every 18 - 24 months something will trigger his anxiety and I'll be darn if every symptom he's every had with-every disorder doesn't come roaring back.
I think we would have had even better luck with-the therapies if we had concentrated on motor skills and sensory issues first. (I have nothing to back that statement up with -- it's just my opinion.)
difficult child still has "holes" in his learning and definately is a work in progress. But I know the seeds have been planted and I can hope that someday at least some of them will bare fruit in the future. (Shoot difficult child still attends after-school care. Primary reason? Further development of social skills.)
Age-appropriate maturity is also a problem for us. It can't be "fixed." I've come to believe that difficult children' develop in their own time.
I do believe that no effective treatment can be found for some kids.
I think it's just as hard to answer the question of, "How would things be if we'd never tried intervention or treatment?"