Oh I completely feel for you. This happened to my DD a couple of years ago. She got covid and was very unwell with it. She missed 3 or maybe 4 papers I think from memory
Pushed herself to go in for English as the school recommended but felt far too unwell. She could barely read the paper, attempted to answer one question and walked out. School contacted the exam board and we sent a medical certificate but they weren’t terribly reassuring tbh and said it was out of their hands and up to the exam board.
It was such a worrying time and we weren’t expecting great results as she’d been sleeping between exams not revising but it actually turned out okay. She got what she needed to go on to A levels which really is all that matters. We had fully expected she may need to resit especially English but because she’d already sat one paper, they use that to work out an average grade and she ended up with a 7 in that which she was happy with.
Try not to worry too much. I think if he can manage at least one paper per subject, you might be okay. as they will take an average. You absolutely will need a doctors certificate so that’s priority.
I totally understand, they work so hard and then something happens out of their control but if it’s any reassurance, the exam board were pretty fair in our experience. Good luck 🤞