OP
This isn't going to sound good but keep reading.
If he gets any grade at A Level then he has a 'full level 3 qualification' so no more funding available.
But he has options.
He could resit as a private candidate, so he would be studying on his own, if her does this I would suggest only doing 2 sunjects.
He could start a course with the OU and then possibly transfer to a brick uni.
Or he could study with the OU and take his degree with them, if there are medical needs, which there seem to be then he could get full funding.
I'll be honest I'm studying with the OU so I am biased.
He could start an apprenticeship.
He could work for a few years, if he is only just accessing the help he needs it might be the best option.
If you can afford to support him he could do some volunteering.
Foundation years are another good idea, make sure it is a 'foundation year' not a 'foundation course'.
If he takes a year or two out then have a look at universities that have more open entrance requirement or if they have colleges have colleges for older students, Harris Manchester college at Oxford has an open day in a couple of weeks.
https://www.hmc.ox.ac.uk/event/open-day
https://www.ox.ac.uk/admissions/undergraduate/applying-to-oxford/mature-students
This is not the end, this is a new start. Some people go through school, college, uni in a straight line, others, me included, take the longer prettier route.
We get to the same place but slower, with more memories and more experience.