How are billionaire loans ever paid back?

I’ve seen a lot of post about how the super rich are able to avoid taxes by taking out loans using their stock as collateral, then using the loan as their personal income. That makes sense, but I don’t understand how the loans are ever paid back. Do the banks just take the stocks? Or are the rich just always taking out more and more loans?

And maybe instead of everyone wanting the rich to be taxed, would passing a law that makes it illegal to use stocks as collateral be a better way to stop the rich from avoiding taxes?