I’ve known a student in this position who would have got the place if they had missed their offer by one mark (based on that happening to other students in the same position) but when applying with grades in-hand didn’t get an offer, as one grade below the standard offer. Later that course was in Clearing again, but by then they’d decided to go elsewhere.
Not sure it helps OP, but for anyone reading who is considering having a year out and applying with grades in-hand, bear in mind that most predictions (that those yet to sit exams apply with) and wrong - over 80%, with most being too generous. That means that the grades on your application pre-exam are likely to be better grades than most will have if applying post-exams. Often getting the offer is the key…because many will then let someone in as a near-miss, but simply won’t offer in the first place with the lower grades.
All this said, the less competitive the course, the more likely they are to take the applicant who has grades in hand which are very close to the standard offer, if they know that historically they accept that or less. So on this occasion I’d say OP’s son has a v good chance.
For anyone in yr12 who wants to apply for a competitive course at a v popular uni, applying with those likely higher predictions pre-exam is a good idea in my book, unless of course they just don’t know what they want to do. Even v popular courses will often take a near-miss rather than ‘risk’ Clearing, when it’s uncertain if those provisionally offered a place then will actually take it, or if good candidates will emerge and actually convert into bums on seats.
Bear in mind, very popular courses are unlikely to let you defer if you achieve less than standard offer - they take their chances with next year’s cohort instead. But, not so competitive courses might well agree to deferment.