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?
As frequently noted here the definition of "Autism" has changed, and now folds in Asperger's Syndrome. You're talkin' old definition; but even then you're assuming no compensating features in relatives (which the multiple-copy alpha tryptase genetic trait, to name one likely suspect, almost certainly confers.)
A stark reminder that not only do people who think like this exist, they express it freely in public. While there is a discussion to be had around eugenics, that attitude is not it.
If women have a right to terminate a pregnancy within whatever time limits society imposes, should society also impose motivation limits? That sounds like a very slippery slope.
Hey guess what? I've had friends with autistic kids. It ruined their relationship with their "neutotypical" offspring, who says the same thing (and now no longer talks to her parents).
Some people's only real purpose in life is to serve as a warning to others; the people who raise a severely autistic child are in that camp.
We only have to put up with this until there's a screening test. Then the problem will take care of itself, like the way Tay-Sachs is disappearing.