I-140 Approved Change Visa to G4

[richess]

I have approved I-140 and am currently working on H1 visa in the US. Now if I take up an offer with one international organization, I would need to switch to G4 visa. I have got a couple of questions - 1) If I switch to G4, would the I-140 still remain valid? As I understand, because of the new rule the employer cannot revoke the I-140 any longer. But I have also come to know that green cards need to be surrendered before switching to G4 so since I-140 is part of the GC process, does that get automatically cancelled if status changes to G4? 2) If after few years I want to switch back to H1B, would I qualify as cap exempt because of the approved I-140? Is there any time limit by when the switch has to be made?