But if the cause is genetic and is due to a particular combination of otherwise harmless or even beneficial genes, as it has been speculated here in the comment

But if the cause is genetic and is due to a particular combination of otherwise harmless or even beneficial genes, as it has been speculated here in the comments, then autism itself won't disappear. What would disappear is the need to care for such a child or to watch it deteriorate and die early as with Tay-Sachs. I.e. basically a Spartan way to deal with this. Is this what you meant?