And by that, I mean the oligarch's fortunes, personally.
I'm sure the Ivy League Lawyers -- threatened that the endowments of Harvard, Yale, Princeton, etc. would be summarily seized by the government otherwise -- can find a way to get around the explicit Constitutional prohibition on "bills of attainder"...just like they ensconced a mere penumbra into the inviolate right of abortion, and eliminated the "Shall not be infringed" part of the 2nd amendment.
The tax breaks that Warren Buffett relies on can also be revised or repealed. After all, he has invited “soak the rich” tax policies. He and the other Lefties can be made to go first, not through bills of attainder but by attacking the tax breaks they exploit.