This is accurate; no one outside the family would have been able to use the client base.
No matter what you’ll lose clients, but lose a lot less than if Alice disappears one day and Bob magically appears the next with little handover.
Dunno if that could work in Japan.
I know a printer right now where the owner has been working towards retiring and selling the business to his now-manager eventual-successor for a few years. The owner has reduced his work responsibilities to sales only at this point, and the goal has been to make his networks comfortable with his successor as he slips away (to live closer to his grandchildren, I bet.)
So it's still the same family!