I see tanks of them in fish shops all the time with their backs bitten out as well as other injuries so I know if they can do that to each other then they can really massacre any dentitionally unmatched fish.
He will die if you don't rehome the piranhas unless you want the piranhas eat all of your tankmates. You don't think that the piranhas won't attack again after the first incident with the jag?Thats why I included monster fish keepers in on this. It was literally a fleshly hole. he couldnt eat anything and had no lower jaw. just a hole that could not close. I thought it was really amazing as to how much it grew back, to look like it does now. I really thought he was gonna die.
Keeping piranhas with other fish in a tank is borderline cruel. In the end the piranhas will slowly kill and destroy everyone else. Its usually one day you forget to feed then someone disappears, or if a fish gets sick they will take advantage. It may workout short term, but never in the long run, be prepared for more missing fins, and inevitable fish loss.