It is still difficult to see the actual involvement of the bone, i.e., how much is left, if there is still another piece somewhere else, if there is any necrotic tissue, etc. More than likely, the only thing that can be done for the bird is to treat for possible infection, which without a blood test, can't be determined. Yes, they may euthanize him if they feel that the bird is suffering. You usually can determine this by the weight of the bird and if by touching the area, the bird reacts strongly to pain. Even if there is not infection, pain can cause the bird stress, cause it not to want to eat and eventually, it will die.

Birds are strange living organisms. They can go on and on appearing that everything is just fine (this is nature's way to hide any illness or injury from a potential predator) until they suddenly keel over from fatigue, stress, starvation, infection and die.

This is a hard case to determine if anyone can help him. Is there a wildlife/waterfowl rehabilitation facility that might keep him as an educational bird or a waterfowl farm? Again, they could take him in and he could still eventually die within the next month based upon how involved the injury. At this point in time, he does need to be captured as this could be a very long and painful death as the other geese or a predator will eventually get to him if the ensuing injury/infection does not. The Regal Swan