Different circumstances but a bit of a positive story:
I did really well in year 11 and 12. Great GCSE grades and AS levels.
However, when it got to year 13 I became quite poorly. My attendance was around 40% due to having lots of time off due to the illness.
I had to drop a subject as I just couldn’t cope with the work. I had to re-sit year 13 as I didn’t have enough UCAS points to go to university. I was gutted. Felt like a failure. Most of my year were off to uni and I was stuck re-sitting with classes full of people a year younger than me. I felt really silly and sad for a long time.
However, I worked my socks off, picked up an extra subject (wasn’t an A-level, more like a BTEC which was all coursework based, no exams) and managed to get enough UCAS points to go onto a foundation degree. The extra year also gave me time to work part time and save up.
If your DS works hard, asks for help, accepts help and guidance from his tutors and takes every opportunity given to him I’m sure he will absolutely fine. He needs to remember that grades aren’t the be all and end all of life. There are so many gateways to so many careers.
I wish him the best of luck x