From other reports on this forum, if you get off the plane during the stop in YVR -- and it doesn't seem to be consistent whether people are booted off the planer or are allowed to remain on board -- you're stuck in the holding room by the gate and can't go elsewhere in the airport. Mind you, at that time of night, everything in the international departures area in YVR is shut down. They even turn off a lot of the lights!

I've only ever flown the YVR-HKG portion of CX889, but when I was boarding I remember seeing a bunch of tired looking people (sheep?) stuck in the holding room by the gate.