I am there to operate the Aircraft in a safe manner according to all the rules of aviation...airspace and sops and manufacturers guidelines etc etc etc....there is no way in the world I would ever come out of the flight deck to attend to any situation in the cabin.....there are all the normal procedures in place and CC training and if after all this the situation cannot still be contained/resolved depending on the situation I will divert but going out of the flight deck in flight is certainly not something any pilot should be doing...and if i was a pax on this flight its certainly not something i would even want to see.
CC can try and resolve etc using their training and sops and procedures..they can give the pax the written warning from the captain explaining that if they don't comply the aircraft maybe diverted or they may be arrested on arrival. CC can ask for assistance from pax if required....and if i was to intervene at all the only thing I would do is from the flight deck make a PA to remind the pax that this is the Captain speaking and if you dont comply with the instructions of the CC then I will have no choice but to divert immediately and hand the matter over to the airport police etc...but opening that door is 100% never going to be an option...it might be a ploy with a group of 4 terrorist onboard...one play the fool and lets hope the Captain comes out as the others are seated in row 1 ready to charge the door...anyone leaving the flight deck should give their licence back.