for the most part it should heal on its own. Just keep an eye out for infection rredness things like that. now you have to address the aggression problem ideally I would suggest separation if that's not possible larger enclosure. it's not fair to the ones being bitten to keep on being bitten know what I mean.
Now that it has been injured, if you leave it, that tail will only get shorter because the other turtles will keep picking at it. As dmmj said, go ahead and separate the turtles.
--Berkeley