The reason I asked is drakes when starting into hormone crazies have been known to mate and try to mate with hens and it can lead to serious injury or death to chickens. I have never seen one of my drakes drag one of their ducks into the pool but they can sure be rough with them. Keep an eye on your drake and your chickens he may never try mating with them since he has a mate but one never knows. And she could have flown into the pond as duck mad said,
if you want to try to encourage your ducks back into the pond ,maybe tossing something they like to eat into it may help. shredded lettuce or dried meal worms