Glad to see he's dropped the A Levels and is starting again with the Btech. I guess this also means he won't be getting uni predictions now, but will wait until this time next year to apply for uni, after his second L6th.
Another useful thing for him over is summer would be to look at uni courses and requirements from Btechs. If he gets a sensible idea of where he would like to go and what he will need to achieve, he will have a good focus from the start if the new course.....this is what he was lacking this time round. Seeing his friends who are in Yr13 applying to uni and being stressed about applications and results will be no bad thing either, as it's all a wake up call to what will happen to him the following year.
Other things which might help, include him saying to his Tutor at college that he is keen to avoid a similar thing happening this year and would like regular meetings to honestly discuss progress - perhaps weekly or fortnightly - wanting this would be a real sign of growing maturity. I know colleges are more 'hands off' with parents than schools, but as parents Inwould also be looking to be in more regular contact - so when he's heard back about the Btech, as parents I would also send an email and copy in all the relevant people, saying how it is a real shame he wasted this last year, you are glad he's taken advice to do the Btech and is hopefully going to be more mature in his approach, but you would also like to keep in touch with college more to check things aren't slipping.
It is about being happy.....but also about being productive. It's great he's getting a second chance, but really important he doesn't squander this as well.....it's very easy for weeks to slip by without really knowing if things are going well or not and a crisis forming before you know it's starting, so I would say it's worth talking with him about the danger of this and the importance of both him and you being in regular honest conversation with the college to avoid it. Has he had a genuine scare from what has happened recently, or is he still happy-go-lucky head in the sand and likely to be similar?
Once you hear back about the Btech, you could always ask if there is any preparatory reading - that would be more focused and useful than returning to stuff from a different course.
Glad things are moving forward in the right direction....now to keep them going that way....