The net worth is simply the sum of assets minus the sum of liabilities. Take away the assets and you take away the net worth. I can't think of an asset category that you can't transfer if you are willing to sacrifice its value (which presumably doesn't matter, because it's not real anyways)

In the rare cases where contract law makes the transfer impossible legally the government could trivially step in to make it possible

You take control of the shares and distribute the proceeds and make it impossible to leverage them for loans, credit etc.

Is it Zuck's networth or salary that makes it possible for him to own his ranch in Hawaii?

Why not? Net worth is the estimated sell value of a list of assets. It is entirely possible to take those assets, or charge a tax based on that estimated sell value. Why would it even be a little difficult, let alone impossible?

And certainly ceejayoz was being a bit glib by suggesting we take all of it, but it would not be remotely insurmountable to tax billionaire wealth.