I'm sorry to hear that you found a compound fracture. Setting the bone after so much time is probably not going to be possible because both broken ends have probably already begun to heal. The choice becomes can you keep him separated for possible the rest of his life? I'm not trying to scare...
Is the leg broken? Did you palpitate to feel for broken bones or chips? Does the swollen part feel hot to the touch? I personally don/t use antibiotics in waterfowl because it seems to slow their healing time (in my personal experience-read opinion here). But I have noticed that ducks tend...