I don’t have a child with ASD, but I know a LOT of ASD kids. And they don’t seem to fail to thrive any more than non-ASD kids do. One of my kids had an awful time for the first few months of college. For the first three months, it seemed that every day brought more texts of doom and tearful phone calls. She stuck it out and is happy now.
There are so many kids that have to deal with myriad issues: homesickness, loneliness, lack of motivation, excessive partying, financial troubles, medical issues, family problems, mental health problems, various learning disabilities, you name it. Yes, ASD is an issue, but in my opinion, it’s not vastly different or worse than other things that college students have to deal with. The point is that virtually all kids will face challenges when they go to college.
OP must have felt reasonably confident that her son could handle going away to college, or would have never considered it in the first place. I suspect that reality is hitting home and the “what if’s” are creeping in. The classic saying is “What if I fall?” “Oh, but my darling, what if you fly?” Let him fly, and if he falls, help him get back on his feet.