Sending you all big hugs as you deal with these challenges. I have a friend who is navigating this and struggling.
I'm assuming that my brother and sister-in-law went through this process with their youngest daughter (who is now 42), although maybe laws were different then. I know that they have pretty much spent their entire lives advocating for her needs, through school and beyond. It's been a labor of love, but also incredibly challenging. Intellectually, she's probably at about age 8. While she's not truly independent, she lives in a home that my brother and SIL manage as a nonprofit, called A House for ME. They knew that they wouldn't be around forever, so they needed to figure out how to best take care of Dana, since the wait list for housing here in Maine is ridiculously long (as I'm sure it likely is in many states). Anyway, Dana and another woman live in the house with a caretaker. Dana has a full time job at a nursing home, where she has been for many years. Although she's never going to be truly independent, this arrangement has been wonderful for her and everyone involved.