This issue really isn't far removed from inheritance enriching their children, and the solution is the same. The price of life extension has a tax imposed at a rate proportional to your net worth.
I cannot believe inheritances aren't taxed in many places. You work hard for your money, it gets taxed. You get a windfall you didn't work for, it's tax free. It does my head in. It appears to reflect the will of the majority though, so in that sense, for inheritance and life extension alike - you get the outcome you deserve. If people insist on no taxes that target passing on of wealth, then they will have to live with unlimited accrual of wealth at the top.
Most people don't really look into the issue in detail. Any time a significant inheritance tax is threatened they can just roll out stories of bereaved children getting told their parents have passed away and immediately receiving a massive tax bill until it become unpopular.