I would keep the duck until its flight feathers have grown in so it can relocate easier and seek out a new habitat and flee from predators. Your duck lacks experience and the protection a group of siblings and other conspecifics would offer.
You could also try to contact local birders, I could...
Although I normally would endorse adequate company, another duck would only be a good idea if Julzz would be willing to keep it after the release of the ring-necked duck and for that reason not only one but two ducklings were aquired.