PIP assessment

Hi - apologies for the long post

I’m just looking for some advice regarding a PIP assessment booked for next week. 

Its for my son (diagnosed with ASD/ADHD/anxiety).  He is 25 and was awarded PIP three years ago. He’d had DLApreviously but stopped claiming when he insisted on being normal and managing without! But at Uni his advisor suggested he claim again and he was awarded without a face to face assessment.

since leaving Uni he has struggled hugely with life, the world etc but we have a great GP and had some advice from CAB etc. 

He claimed ESA initially whilst looking for work but after a  face to face assessment they put him on JSA - followed by constant stress and difficulties with that situation. We appealed and the Uni also helped and the decision was reversed. So back to ESA. 

But then PIP now decide they wish to reassess and we have been given an appointment for next week. I can take him but the stress before plus meltdowns after will be immense and he will take weeks to recover - not to mention overthinking every possible (and not possible) outcome! He will also sit and talk to the assessor but refuses to talk to a stranger about his difficulties. It’s taken years to get him to a gp he will talk to. 

I wondered about asking for a paper based assessment but is this still a thing? I guess Im concerned as he will be able to go, and have a conversation but they will not be able to get a full picture of his issues. I will be providing them with a letter from the Uni but not sure if that’s any help.

i guess I’m just looking for any advice

apologies again for the long post!