How can we determine if our son is completely insane and unaccountable, or partially insane and accountable, and is it permissible to wish death upon him?

We previously referred the questioner to the definition of 'mentally incapacitated' (ma'tuh) so she could assess her son's condition and determine it herself. Otherwise, she should seek assistance from doctors and experts to ascertain his intelligence quotient and comprehension. As for wishing for his death to be rid of his harm, this is not appropriate. What is desired is well-being through his rectification or his recovery, so she should supplicate to Allah for that.