Sadly, when birds are injured treating them is difficult and oft times futile. However, unless internal organs are visible, or the bird appears in major respiratory destress I would try to treat them. It is amazing what they can come back from. Isolate the bird, clean affected area with something like a betadine solution. Then cover open areas with an antibiotic ointment. Even gaping wounds can be sewn up and treated. Insure the bird is kept in a clean dry area and add an electolyte to the water. I have had good success using Poultry Drench.
I personally would not take a bird to a vet. I can't afford spending in excess of $100 on a $10 bird. If I don't think my treatment will be sucessful I don't hesitate to cull.
Best wishes and good luck