I did Business with a marketing pathway (2 yrs of marketing), the choice was marketing, hr or finance. It was also a sandwich course with a year in industry - this gave me and my peers work experience advantage over other graduates, or offers of employment post graduation (presumably DS will need to fund his business). The degree gave me a rounded understanding of how international businesses work, reading financials and P&L sheets and the economy.
I did a CIM postgrad a few years later, which opened many doors and made me a better marketer.
Some unis offer a top-up to make your CIM postgrad a masters but I don’t think it’s necessary, there’s loads of useful vocational qualifications around marketing disciplines to keep up with trends and developments.
I would love to do an MBA, but for DS I think this would be unnecessary until he’s got some work experience and is looking to take his business to the next level eg venture funding, gaining large overseas market share etc.
Also, look at where his tutors work, have worked, if they still do a lot in industry.
Lastly, have a look at Cranfield Uni. Highly respected in business world and home to Malcolm Macdonald (pretty sure every marketer has studied at least one of his books)