Traveling outside US & returning back with approved I-140, waiting for PD to get crnt

[aidonaj]

Currently on H1B visa. 3 years expires in Aug 2016. Possible to extent another 3 years upon expiration. Employer has filed for I-140 which is approved. Now, the situation is, I am migrating to Australia with my wife on PR basis. Will need to stay at least 2 years there. During this period do I need to keep my H1B current? Can I stay outside US based on approved I-140 for 2+ years and then come back to US when the priority date gets current? such a big dilemma for me. Plz help !!