He's insane and taking a massive risk.
Loads of people who owned small shops thought exactly the same in the 70s and 80s and found themselves stuck when they came to retire as their shops were unsellable, not even as empty properties, and those who "lived above the shop" in flats were even worse off as they were trapped there. Mostly they had the same idea that they'd just sell the shop and live happily on the proceeds, buy a bungalow or flat, go on cruises, etc. The reality was an empty ground floor shop slowly deteriorating.
There are still some like that now. One guy ran a thriving TV repair and electronic component business including a shop, several staff doing repairs, he and his wife lived in a really nice flat above the shop, and all was hunky dory. Now, his wife has died, the shop and flat are virtually derelict, he's living in squalor, the shop is still full of antiquated electronic components that are gathering dust. He had it on the market for 20 years and didn't even get any offers, and only a handful of viewings over those years. That's literally tens of thousands of pounds of components (at cost price, not current value which is probably only scrap value) and a property that he has no money to renovate which could be worth £100-£200k once done up (new roof, new windows, rewiring, central heating, sorting widespread rot etc).
It really is 50:50 whether someone will be able to sell a business these days. All it needs is a change of regulation/legislation or a change in buying habits or a change in technology, and the value could drop over a very short timespan. Even worse would be some kind of catastrophic event, like an insured claim for damages or a big customer going bankrupt and the business itself could go under, leaving nothing to sell.
Please, please, knock some sense into him!