Hi there,
I would imagine your drakes will probably get on OK now if the female has abandoned them to sit on eggs, although from what I've seen of Call Drakes, they can have quite a temperment, so who knows!
As regards your ducks disappearing, this is an interesting one. Last June we got a pair of Call Ducks, a duck and drake. They were able to fly, and didn't settle with us, but went to live with a family of 5 ducks down the road. These ducks were much larger than the Call Ducks, and were not particularly nice to them, but they still preferred to be with the others, rather than live with us.
Come the end of the summer, the folk that had the ducks down the road moved away, and we thought our Call Ducks might come home then - by this time we had a gaggle of 8 young adult Shetland ducks. But the Call Ducks never came. We went down the road and fed them everyday, and tried to get them to come home, but they just got angry and flew. We never cut their wings for the same reason as yourself - except the main predator here is otters.
At the end of September the female duck completely disappeared, and the drake was left forlorn. We felt awful, and were all set to get him another companion - then he disppeared. We had no idea if they were taken by something, or if they had flown away. Exactly 6 months later at the beginning of April this year, who should appear in our backgarden, with the rest of the ducks, but our Call Drake! We were overjoyed to see him. He now comes and goes as he pleases, and joins the rest of the ducks at feeding time - but he has no mate. He has also recently started trying to mate with the bigger ducks, so we are on the look out for a new female companion for him. We have no idea where he has been. It has been a really cold winter here, and we have have had lots of snow, it shows how resilient they really are.
Although I don't like the idea, if we get a mate for the call drake, I think we'll be cutting her wings, as I think they do just take off, I've heard this from other folk that keep them. Hope your ducks come back.