I think the GWP would have to go back. I've never been in this situation but my friend told me that they asked her for the GWP back. Is this from a department store counter such as Macy's or Nordstroms?
One employee at a Clinique counter at Macy's once told me that people were abusing their GWP by buying the minimum purchase in order to get one, then return the purchased item and say they don't have the receipt so they could get store credit and get something else with it. The customers would also keep the GWP. Now Macy's is getting smart with it. You know know they manually put a return sticker on each item you buy? Well now if you buy something and there's a GWP, they are beginning to highlight the return sticker of the item you purchased with a highlighter so if people do try to return the purchased item for store credit without a receipt, they'll know there was a GWP involved. I hope that makes sense!