Qantas has not announced they are leaving OneWorld. The Qantas and Emirates code-share 'alliance' won't change the lounge access at Hong Kong.
Yes: "Customers flying First or Business Class have access to the equivalent class of lounge regardless of their frequent flyer status."
http://www.oneworld.com/ffp/lounge-access/
I've never understood the point of the QF/BA lounge in HK. Who in their right mind would sit in that mediocre place when there are various good/excellent CX lounges within walking distance?