another (grim!) consideration - if I understand correctly, you could be left with just one duck that you will treat? Its stressfull enough doing this (trust me... and can be a very messy, muddy job!) but that little duck will nobody to tell about it.
Amd if you then want ducks to replace the ones lost, that poor little duck will have the added trauma of adjusting to new "friends" in his/her house.
so even if the duck is potentially healthy, thats alot for it to deal with...
never easy to decide, cruel to be kind is a good maxim, imho
best of luck, whatever you decide