Usually something like that should lead to an incident report to the relevant authority and a case of "reckless and careless" endangering the passengers which in turn would lead to a pulled license. And rightly so. Yes, the supernumary had some limited flying experience in slow and lightweight aircraft, that doesn't really train him to operate in a jet even as PM without quite a bit of additional training (jet conversion course, type rating, base training). However, one has to wonder why the FO vacated his seat when being asked by the captain and thus allow this farce to play out.