Greene, for a variety of reasons, could no longer meet Chris' educational needs. I usually am a fan of partial mainstreaming for kids like Chris, depending on the school. (Children on the spectrum are more prone to bullying, but they're also prone to imitating the behaviors of those around them and normalizing them.) Bob would have made more as an engineer than Barb would have made, and I'm pretty sure she would have been able to get an entry level position like that wherever.
Legitimately, I don't understand why Barb didn't have Early Intervention services if she cared so much. He would have qualified for PT/OT/ST for free until he was three in Virginia through Infant Toddler Connection. That would have carried over to the same services at pre-K, likely with the same people, and those referrals are made through UVA, and he would have been referred to UVA by his pediatrician when he failed to hit mentioned milestones, because as far back as 1985, AMA standards mean his ped would have been documenting those assessments. This means either she didn't take him to the doctor or she flat ignored the referrals and assistance. (And yeah, in the 1980's, moms did the appointments, so I'm pointing the finger at Barb.)
And while it isn't fair, moms just know a lot of extraneous bullshit about their children.
Before taking another mortgage against the house, Barb could have thought about Chris' future and bought a small condo, or even had Rocky set up a trust for Chris, used Medicare to get her in an assisted living apartment, and had Chris live with her. Bob tried to set up a career and future for Chris, although unlike Greene Co., the other school system just gave Bob asspats and said Chris was fine, rather than really evaluating and helping him. Barb has yelled at trolls for bothering her, but did she ever try to negotiate for Chris on his behalf?