If his bike is made for 650C, 650B won't fit and the brakes probably won't reach 559. There are still perfectly good 650C tyres out there for the kind of bikes which have 650C wheels.
The frame will obviously accommodate 559 rims, and swapping from racing calipers to touring ones will fix the reach issue, but who wants to fit MTB wheels to their race bike?
If his bike is made for 650C, 650B won't fit and the brakes probably won't reach 559. There are still perfectly good 650C tyres out there for the kind of bikes which have 650C wheels.