The scenario that I proposed was entirely hypothetical, but I image that they are revoked in the same way that any credential is revoked: if asked to verify that an individual holds it, indicate instead that they don't.
I mean, this has happened a number of times to doctorate degree holders when it was later discovered that they falsified research for their dissertation.
Yeah, but publishing a statement that announces that you're a cheat, and that your education is a sham, actually damages your reputation and your career. Cutting up some paper so you can be debt free would just show that you're not a complete nit.
Even if you actually needed that paper to prove that you are in fact qualified, an entire industry would appear overnight dedicated to providing certified copies. The free market ultimately decides what credentials to trust.
I mean, this has happened a number of times to doctorate degree holders when it was later discovered that they falsified research for their dissertation.