Yes, you can get off in YVR (you might be required to get off, I can't remember). However, they hold you in the departure gate with basic refreshments and basic seats. I.e. no lounge. If you can get availability, you'd be much better off on the direct HKG-JFK service. If a lounge was available at YVR, then it would have been OK. Sitting in the crowded departure gate for an hour and a bit was less than fun.