Inattention when UC50 was filled in & WCA tomorrow

Hello there,
I've just subscribed in a desperate bid to save my friend from his ESA claim taking a turn for the worse at his WCA tomorrow and I couldn't find answers to the questions that are bouncing about in my head.
My friend has a background of suicide attempts and severe anxiety and depression. His last one was an overdose of prescription drugs in 10/2017 when he found himself unable to cope with added stress and chaos at work - after he had to take over workloads or people whom the organisation could no longer afford to keep on - and an ongoing battle with his ex-wife regarding contact with his son. He has been claiming UC since then and has been providing fit notes etc as and when required.
I've found out earlier today that he has his WCA tomorrow lunchtime (I am accompanying him) and that he hasn't got any idea if he filled in a UC50 ("there was some long form I filled in but no idea what it was called or if it was, indeed, for the current claim or the previous one!") nor what the questions/answers were. I'm on ESA (support group) myself and am only too aware that this could turn into a disaster!
I am wondering whether any of my ideas could work to work towards some damage limitation:
* Is it possible to download, complete, print and sign the UC50 and take it with us to the WCA?
* I am working on the presumption that we won't be able to initiate and have ready any substantiating medical evidence to hand in at the interview, especially knowing that his GP works only 2 days a week, BUT would it perhaps be possible to send/hand/fax such information AFTER the WCA to help the DWP decision maker with their decision?!?
* Is there any way that the appointment could be postponed (they cancelled once, and my friend cancelled once)?

I can't think of any other last-minute measures that could help prevent having to go through an appeal process.
Does the fact that he is also in receipt of PiP make any difference?
Also, after having another look through all the online UC profile tasks etc we can't find anything about a UC50, however, that said, the WCA booklet that was sent with the appointment letter mentions the UC50. Tbh, at this late a stage it probably makes little difference whether he has or hasn't filled it in, safe to say that asking someone with severe and acute mental health issues to actively engage with even a take-away menu would constitute stress at the time. And now, me bringing it up is making him so anxious that I feel like I'm walking on eggshells, trying not to say anything that could make matters worse.
I would greatly appreciate any input at all, and if possible before 13:00 tomorrow (10/10), though I know that's probably being a bit hopeful, but hope does proverbially spring eternal, does it not?!?