OP: don't despair.
My son was one of those kids who was normal one day, had MMR vaccine - literally within hours was never the same again. That was 1994. Aged about three he was diagnosed with atypical autism - he has a couple of other things going on as well - dyspraxia and some un-named muscular thing that gives him floppy muscles and makes even doing nothing pretty exhausting. 6 other kids injected from that same batch went on to become autistic.
He had a number of words when he was one, but then he lost all his language and wasn't to speak again intelligibly, til he was 4 or 5. He screamed. All day. Every day. When he was 2 and a bit, or nearly 3 I had him statemented by our Local Education Authority and he was in a special school's nursery unit from then on. They had the right specially trained teachers there (in the time before the special schools were closed down); he was in a class of 6 kids for years, and he thrived. He slowly got able to communicate.
Like a lot of autistic kids he was unusually good-looking. In most situations, to an outsider, eventually, he wouldn't appear 'autistic'. People think of 'Rainman' which is totally inaccurate. My son is actually quite social - once he found his niche (with the arty, indie kids).
When I used to get him ready for that bus to special school I wanted to cry some days. We'd never know what he could have been. I think we mourned for him as if the baby we'd had had died because this child was so different to that baby. Literally the diametric opposite.
It was a stressful time. Our marriage broke up (a few years later we got back together but in the meantime we lost our house and everything we had ever had). A teacher at the special school said to me once our son was the only kid left in her class that still had a mum and a dad at home. Before we split). I remember the day we got the diagnosis, we walked around the shops, just numb. Shell-shocked. I think we were numb for years.
I also remember when putting him in his little coat every day, wondering what his life would be like now. His older brother had an IQ through the roof and even from being a toddler was clearly destined for good things. His younger brother had everything going for him. But my autistic son? Who might he have been? If you had told me then, in 1995, that one day my son would be who he is now and where he is now - I would never have believed you.
When he first went to school he wouldn't talk, would only eat white, dry foods - a teacher sat with him at lunchtime. Slowly she got him to eat normally. Slowly, they got him talking. Slowly he started making friends.
Sadly the special schools were axed and at 11 he was thrown into the mainstream which was a nightmare for him. Away from all his old friends and security and teachers who were trained to deal with him, and none of the things on his statement being provided any more, he had a hard time. But a year or two went by and he found his friends - those quiet kids who like animes, and Art, and spent breaktimes in the library. He couldn't read til he was 17. He left school with no GCSEs whatsoever. He is intelligent. But has whole areas that are blank.
What is his future? Well he went to college and that was the making of him. He did Art and suddenly, he was surrounded with kids who 'got' him, didn't judge him, didn't care he was autistic... He truly has more friends than my 4 non autistic kids put together!
And last year.... he went to university! He was 5 years at college slowly getting BTECs to do it. The first time a lecturer mentioned the word university to us, we did a double take.
He has Disabled Student Allowance, and is about to get a lot ore help kick in for next year. He has lived in Halls all year and made friends he is going to live with next year. He goes out. He is obsessed by Game Of Thrones. He does Cosplay with his old college friends back home.
My only regret is my dad didn't live to see him go to uni. He was the apple of my dad's eye.
OP you cannot know what the future holds. But when I was precisely where you are now - if someone had said to me "You know he's going t be alright. He's going to grow up, be surrounded by friends, and good people, and he's going to go to uni" I would have never believed it. It seemed all that was in store for my other kids, not him. He couldn't speak, read, or write, FFS! Now my other son tells me when they were at college he would never tell his friends he was autistic. Most people figured it out eventually. He hated high school but loved college and uni and he has now found 'his people' and his passions. It will be hard for you. But don't think a single door is closed to your child. He may surprise you and kick a few down.