No, I could not be prosecuted or disbarred for failing to report a client’s intention to commit a crime. In fact, I cited to the Rules of Professional Conduct, which are the ethical rules passed by the bar, not to “the law.” From Rule 1-100(a):
Thus, the rule I cited was an ethical rule, not a legal rule (the law that would govern would be the sections of the Business and Professions Code governing the attorney-client privilege). As the Rules make plain:
Thus, as a member of the bar, my duty is to obey both the law and the ethical rules. Violation of the law (particularly if it is a crime involving moral turpitude) could get me disbarred; violaton of an ethical rule similarly could be grounds for disbarment.
I think your question is whether my legal duty ever conflicts with my ethical duty. It’s an interesting question, and I’d suggest you may find some takers in GD. Although I suspect that the discussion would end up being about Sarbanes-Oxley, which can require a lawyer in certain jurisdictions to violate ethical rules to satisfy SOX requirements, in my (admittedly under-educated) opinion.