Are you giving up on the process? If you are, then turning in your green card shoudl absolve your sponsor. Else the sponsor is on the hook until you reach citizenship or work 40 quarters.
With the green card you don't need to be with yoru EX to pursue the process as long as you can show that you entered the marriage in good faith and you have proof like joint stuff.
With a green card you should not have a ban though there are other requirements such as residency to maintain the card.
