Listen, Boris will survive nicely. With his level of celebrity and tennis connections, he is not going to be homeless by any means. Sadly not the first, I think of Bjorn Borg losing millions through his business ventures, Juan Del Potro's dad apparently squandering his fortune and of course the sorry case of Arantxa Sanchez Vicario accusations that her father/family left her "penniless" despite her earning from tournaments/endorsements over 60 million.
IIRC early in their careers, Richard Williams made sure his daughters knew how to prepare their own tax returns , the larger point being they needed to make sure where their money was at and how it was being used/invested.
To put it in a larger context, they can all thank their lucky stars they are not Roscoe Tanner.