I had one of my roosters loose an eye and I tried keeping him for a while but he was very fearful of anything on his blind side. Also he would accidentally kill baby chicks by stepping on them or running into them so I ate him. Your rooster might pull himself together after a while just keep him...
I say go for it, its good for them and they will love it. Just make sure to mash them up good so they don't recognize them as eggs or they might start eating them as soon as they lay them.
I think it would be better to stop turning earlier rather than later so that the ducks have time to orient themselves in the proper position. I have the opposite problem right now with a cat eating the developing eggs but not harming the broody hens.
Oops I just realized you are talking about duck eggs... If they are anything like chicken eggs then I guess you could stop turning them earlier than usual but I have never hatched duck eggs before. Sorry about that.
They breed year round and they can hatch during the winter but usually hens don't go broody during the winter. My old english game bantam hen hatched a clutch in december but that was the only time any of mine went broody in the winter.
they lay 160-180 eggs per year and they are very good for eating although they are not full on meat birds like cornish crosses. I have one and it has hatched eggs 3 times within the past year.
I would say it was Raccoons If you live in North America.
http://www.avianaquamiser.com/posts/What_killed_my_chicken__63__/
One of these dog-proof traps will catch raccoons and possums. Hopefully the other 2 are hiding somewhere and ok.
I have always had better luck when I take them out of the turner and lay them flat on their sides on day 18. Normally you would put water in the tray for the entire incubation process and on day 18-21 you would put even more water so the humidity goes up. If you live in a very humid area like I...