Cliff1975, I'm so sorry to hear about your DS. What a shock for you. However, it's very good that his DOS got in touch with you and that it's all now very salvageable.
Like MJB suggests, it depends on whether procrastination and feeling overwhelmed by work is an ongoing thing for your DS or a first-time one-off.
If the former, do you think your DS might have benefit from regular support from the student disability centre who I think would provide help with structuring work, setting small, short term goals, checking in regularly so he can 'report back' on what he's achieved etc etc? He might need some form of assessment to merit this or maybe his DOS - depending on how good they are - could provide something similar just to help him through this for now.
If it's an unusual problem for your DS, there are all kinds of reasons he may have struggled to get on top of things and then been too afraid to admit this even to himself - not least because the expectations at Oxbridge can be so high . Additionally, it's been the most difficult time ever for students with no easy social network, no diluting of work pressure having fun with peers, endless isolation and assumptions made about how everyone else is doing and comparing yourself negatively.
In 'normal' times, Oxbridge seem to expect students to manage an insane amount of work for some subjects and get to grips with volume as well as very challenging levels of academia. Many students take at least a whole year even to begin to find a way through. This was certainly the case in my day as an undergraduate. But these are not even 'normal' times.
I hope things get much better for him and remember, he wouldn't have got a place if they hadn't felt he could manage. So his college must have really wanted him and will benefit if they invest a bit more support in him at this point, so he can reach his potential.