dreamsbig, I feel for you and your DC. The college application process is hard enough as it is, without adding these complexities.
A few thoughts:
1. First, the category of "a decent college" includes many, many respectable state universities and even community colleges, with which ones being "decent" depending somewhat on what he is interested in studying. The likelihood is extremely high that he will get into an accredited four-year university of some sort. He might find that that is sufficient to meet his needs.
1a. And even if he doesn't, the differences academically are really not that dramatic (leaving aside the top half dozen schools on the continent) in the first one or two years of intro-level and general requirement courses. If he attends a university that allows him to demonstrate what he is truly capable of, his transfer application of strong college grades will trump a poor showing early in high school. That might be the most critical aspect of this pathway: find a school where he thrives as a first-year collegian, and that will open doors both for remaining successfully in that school, and for transferring to a school that better meets his long-term goals and needs.
1b. FWIW, a lot of kiddos discussed on this forum will continue to post-graduate studies. In that case, a successful four-year university experience will be much more important than the name/prestige of the institution. There's always giving him another four years to work out how to do school at the post-secondary level in a smaller pond, and then applying to a slate of dream schools for graduate school. None of those admissions committees will care about his high school GPA. Or even if he graduated from high school.
2. If you've been through the process recently, or have read enough college advice sites, you may know that a lot of the most selective colleges use engagement points as a factor. If he has a short list of schools that particularly appeal to him, you might consider participating in as many of those as he can stomach, keeping in mind that every live interaction with an admissions staffer or alumni host/interviewer is a potential opportunity to shape the narrative so that who he is becomes more vivid than his freshman/sophomore grades. Most of these activities include online/videoconference options.
3. And finally, there are many possible paths to achieve his goals in life. It is easy to think that the paths you have lived, seen, or heard of are the only ones that exist, but that is most definitely not true. University education is very much a worthwhile endeavor for many people--very likely including your child--but it does not have to occur on the time table, or in the sequence, or at the short list of name institutions, that "everyone says" are the correct ones. Better that he learns how to be the healthiest version of himself that he can be than that he get into a so-called prestigious school that amplifies his challenges, fails to appreciate his unique value, and damages his mental health. Given what you have described about him, I think I would prioritize finding university options that are sensitve and supportive regarding his other exceptionality, so that his giftedness is free to express itself fully.
