Did all parties know those tapes were being made?
If not, Trump’s former attorney could be headed to prison. He could lose his license to practice law.
As for Mueller being able to use them, I think Trump’s legal team could launch a serious challenge to the fraudulent nature of the support materials to obtain a subpoena.
A local court may stand behind the subpoena, but I seriously doubt the SCOTUS would.
Criminal Mueller and his team of Hillary-bot law licenses would also be in jeopardy leaking this. Trump should and would go after all of them.