All the other advice is good, and the duck should recover OK as long as their are not puncture wounds you cannot see.
If your dog is attacking your fowl it means it does not respect you as pack leader, or has not been told not too attack the birds or whatever.
Animals don't regard anything as generic, ie if you bought in a new bird and didn't tell the dog to leave it alone it probably thinks it fair game. Whenever anything new arrives on my land I show it to the dog, and point out and say THAT IT'S MINE In a very loud voice!!!
Mind you I have never kept terriers, but I know of a lovely one up at the local game farm which is dynamite with rats and rabbits but wouldn't touch a poult.
All the best
Sue
Dark Brown Eggs