For a while there was a requirement that if a FD member had to leave the cockpit, a cabin crew member had to stay inside the FD to prevent exactly this kind of thing. Given that there have been cases where the hardened door contributed to total loss of airplanes, I thought this to be a pretty reasonable thing to do. It would most probably have solved this particular case quite quickly. Unfortunately, after the initial shock about the accident in question died down and other questions were raised, this regulation was dropped again. Personally I think it would be a reasonable practice.
On the other hand, it is totally unacceptable that a PIC acts like this unless he has very valid safety reasons to exclude a crew member from the cockpit. From what has been reported since, the person in question has since resigned from the airline.