My parents were both teachers, who, before moving into admin rolls (when I was somewhat older) worked in special ed.
My mother later ended up back in a classroom for a period of time with severely handicapped children. Bound to beds and wheelchairs, non verbal, never going to have independence.
For years after she left her admin job she would go back and spend an evening or two every year watching the kids, so the parents could have some sense of "normalcy".
Her lament was what would the outcome be for these children. Because every one thinks they are doing the best for them by keeping them at home, and close. But the reality is (in so many cases) that the plans for "family to take care of them" almost never works out. Years later my neighbor was an older woman, with an adult special needs child. She died, suddenly, from breast cancer. The brother, who was to take care of him, shipped him off to a group home (because he had kids of his own and lacked the time to care for him properly). That poor mans trauma was doubled when his living situation and life and loss of mother all happened in such a short period.
My own family, I have a severely handicapped cousin (who, became that after a high fever). He too is wheelchair bound and non verbal. However his mother, heeded my mother's advice and transitioned him into a group home early. It worked out well for him as he had a more fulfilling life, and the family (sister, aunts) weren't under pressure for his care, rather just rounding out his life. He still gets out a few times a week with them, and is always around for the holidays.
It's a tough thing for parents to understand that what's best for your special needs kid is sometimes going to be harder on them than all the hard work they doing. And I remain grateful that is isn't a choice I ever had to make myself.
It's very frustrating that behind every "you should be eternally grateful for every child no matter what" warm fuzzy message is an implicit "and if you ever express regret for having a kid who wound up non-verbal and violent and destroyed your marriage and your relationship with your other kids you're a horrible person".
Not referring to your cousin specifically but my mom's life's work is with severely autistic children (the "can't talk and hits people" sort, not "I'm a bit awkward and love math and doing anything to help autistic kids is abject cruelty!" sort), and the experience for parents mostly seems to be abject misery.