Every kid is different, let me start with that.
My son, now 17, was diagnosed PDD-NOS when he was 3. That day was the most confused, overwhelmed, and helpless I've ever felt. Like you, I imagined all the worst case scenarios you can. Fast forward to now, and he's in normal classes at a normal high school. He's a good kid and a good student. He's quirky. And he can still get overly emotional when things go off course. But he has learned to adapt and succeed - so hang in there, there is hope!
Get all the help you can - talk to people (like you're doing here), talk to experts, talk to off-the-wall-kooky doctors. Talk to everyone. You will find stuff that works for your son. You will find things that your logical brain says shouldn't work, but you won't give two shits if it helps your son.
We still leverage the public school resources, and also did a lot of therapy when he was younger (ABA was fantastic for us).
Keep your head up, and realize that this isn't the final outcome. But this is the start of a journey that you & your family will have to navigate and complete together.
Send me a PM if I can help.