I wouldn't be surprized if the gosling (if ever hatched) would be accepted by your pair. Adoption is fairly common with wild geese since natural mothers are often lost. Good luck trying to sneak it back if he makes a peep the geese will hear it. He might not accept that he is a goose if you...
This is just my opinion. based on domestic geese (I get the idea that yours are wild type) Usually a mother will return to the nest if there are any living eggs left. Is there any chance that the eggs Hatched that night and the flock is hiding the goslings in the pond? Just a guess of what...