H1B Visa transfer and GC process after long vacation

[km44]

Hi..

 

I am an Indian citizen and currently working in Company A, who is holding my H1B Visa and processing my GC.  I have got I-140 approved. Six years cap is over with my H1B Visa, but I have got another 3 years extension based on I-140 approval. My VISA expiration date is June 2015.

 

Now I am considering pursuing MBA in UK. Since sabbatical vacation is not an option, I need to resign my current company. I have a few questions for my situation.

1. If I resign to my current company, do they cancel my VISA and GC process?
2. After studies I want to come back to USA, so can I transfer H1B Visa some other company after my studies.
3. If I initiate my GC again after my studies (once I am back in US), can I port my GC priority date?

 

Thanks