Does the billionaires (or their kids) eventually pay the tax from unrealized gains in US?

Billionaires can live their whole life on loans with their stock as collateral, but when they die, their estate is taxed before inheritance (and loans most likely paid off). They can set up a trust, but if the kids want to access this money, it is also taxed. So in theory, it’s just a question of time when they pay the tax. In practice - is there any recently deceased billionaire who somehow avoided taxes and his kids can enjoy his money tax free?