I have spoken to DS, who is actually the staff member who deals with mental health issues in his department!
He says, the personal tutor is not the person to talk to as they are not allowed to talk to parents because their students are legally adults - and sometimes the parents are the cause of a students problems.
What they should do is contact the mental health welfare unit at the university and also speak to the 'Undergraduate Adminstrator' in the department he is in.
The one thing he said again and again, is that the university can do nothing about something they do not know about and neither can they do anything in retrospect. If they know a student is having problems, they can postpone deadlines, arrange any support they need and, if they consent let the lecturers who teach them know. They can note that a student has gone through a severe mental or physical crisis and this can be taken into account when marks and degree classes are being assessed .
He said again and again, that they can only help if they know there is a problem and only from the point at which they know there is a problem. There are absolutely no points to be gained for being brave and suffering in silence.
So your nephew should be encouraged to talk to the mental health unit at his university, and let them know the problems he has and about his recent diagnosis. He will not be marked down or written off because of his problems, but will find that the university will do all they can to help him. They do not want students to fail and will do all they can to help.
Ihope this helps.
He is talking about the sytem as it works in his university, but all universities have similar systems.