alt Hacker NewsDebt is usually rolled over if the billionaire is still rich (banks will do that for fees). The only expenses are the interest charges- which were small 3 years ago but larger now because of how interest rate increased.
Re: estate taxes - almost no ultra rich pays them, even without surviving wife. According tom Garry Cohn (former big kahuna at Goldman Sachd and former treasury something or other in the first Trump admin) only morons pay estate taxes : https://www.cnbc.com/2017/08/29/only-morons-pay-the-estate-t...
As per your linked article, they mainly either give away their money to charity, or they set up trusts. When beneficiaries receive money from the trust, it's taxed as income.