In my state it is illegal to divorce a spouse who is in medical/mental health treatment. My friend tried to divorce her abusive husband when he had a stroke, she wasn't allowed and was actually put in charge of his care at the times that he couldn't be responsible for himself! She took her boys and moved into an apartment but was still forced to care for her husband, or arrange for his care. You have to satisfy a waiting period before divorcing and even during the waiting period you can physically separate but you can't separate your finances; so even if they separated, the wife in OP's scenario would still be financially responsible for her husband's care. I would guess there are similar laws that apply to OP's friend's situation, and that is why they don't simply divorce.