I don't believe there will ever be a cure for autism, just as there are no cures for other emotional, personality, and mental disorders such as schizophrenia, bipolar disorder and so on.
I think that ultimately we are going to find that Autism is not really a single condition, but is a group of conditions that result in similar symptoms. I think that we will eventually conquer Autism, but that it will come one piece at a time, as first one type of Autism and then another is finally understood. As others have said, we need to figure out what the cause or causes are before we can even hope to come up with a cure or preventative.
Perhaps there will come a day when there is a cure for autism. Personally, I think that day is a long way off. We still don't understand what causes autism. Is it genetic? Is it environmental? Until we nail down the cause, we can't hope to cure it. I think right now the increase in awareness and the early intervention treatments can help people with autism live better lives even without a cure. Consider that autism is a neurodevelopmental disorder. We still do not have cures for other disorders in this category. For example, we know a lot about Down Syndrome. We can even test a fetus to see if it has the disorder before it is born. However, we cannot cure the disorder and, in some cases, we still struggle to treat it. Humans are simply too complex for there to be an easy answer. I think it will take quite some time before we understand enough about this type of disorder to even begin to attempt a cure.
I do believe thata cure for autism will be found, but not for many years. Before a cure can be found the exact cause will need to identified. There have been many suggested causes but none have been proven yet and until there is a definitive cause there is no way for a cure to be found so a cure will not come for many many years.
There are many factors that will make it extremely hard to find a definitive cause and later a cure. Autism affects people of varied social, environmental and economical backgrounds. It also affects it's victims in different ways, there is not two cases of autism that is exactly the same. All of these things will make it extremely hard to pin point a definitive cause for autism.
The only thing doctors and scientists are sure of is that autism usually affects children before the age of three and continues throughout their lives.
At this point the only treatment for autism is management. Autism can be managed in many different ways depending upon the specific needs of each individual. Social interaction, language, fine motor skills etc can be taught threw intensive special education programs.