Feed him, expect some basic housework and contribution to family life, and grit your teeth as you accept that this is his problem, not yours to solve
Speaking as an academic, that's sort of my advice as well. He needs to learn about consequences at some point, although I can understand the mix of frustration and concern you must feel (we often feel a professional, rather than maternal, version of that).
It's a big consequence though - not getting his full degree. But it's his degree.
What you could do is look at what qualification he'd receive if he doesn't complete his third/final year. There's a national framework of qualifications, and his degree will have accumulated a certain number of credit points.
The standard undergrad Honours degree (in England & Wales) is a total of 360 credit points, with some requirements for a certain number at each level, but most students do 120 credit points a year. So you could do a rough totting up - if he's not finishing his Spring Term (or 2nd semester) work, then maybe he's got 60 from 3rd year, plus 240 from 1st & 2nd years. Total 300 cp. I think (but you'd need to check) he could be awarded a Certificate of Higher Education. Maybe a Pass degree? (but that's a big maybe).
Then you could perhaps shock him with this?
Unless there are mitigating circumstances beyond the ones all students are experiencing, and for which most universities have instituted very generous mitigations, then it may be very difficult for him to get through without handing in the work in August. At my place, he'd have to repeat the whole 3rd year - it may be different where he's at.
But all of these degree and examination regulations are publicly available on university websites.