Your hope should be that they stay healthy, remember, they are part of the little one. So you want all of the chick to remain healthy. Kind of like when you see Siamese twins, you want the whole body to be in good health. I would say don't worry too much. This chick is kind of of Siamese...
I don't think the vet can do much with the chick, if it was born that way. I would let it be, if it is eating and drinking and passing out feces, I would continue to treat it like the others. Sometimes chickens with strange things survive. In any event the yolk would sustain him/her for at...