I'm not sure in that case. Do you have an EAD? Perhaps you could continue using that to work when you come back.How about if there is no unused time? i mean I have used up 6 yrs of H1B already. i am on extensions based on Approved i140
How long before you get your US GC? If more than 5 years, I would move to Canada and come back as a Canadian citizen. Just my opinion