I would argue that the flight attendant should intervene in a potentially intoxicated pilot scenario. Flight attendants are part of the crew resource management paradigm (per the FAR) and have a role in the safe operation of a flight.

In the original scenario (deplaning) I don't think the FA should have confronted the captain. First, the FA has less information than the cockpit crew and, second, the captain is ultimately responsible for the safety of the passengers.