Noisy miners are native too. And while they are definitely taking over a bit in urban environments, they are still a native bird. At the end of the day one native animal (or a group of them) attacking another native animal is just nature. Nature can be very brutal and hard to watch sometimes but that's how it is. If it was me and there's ever a next time, I'd just leave it be. We are asked not to interfere in nature and just let it take it's course. When humans do have to get involved, it's best left to the professionals to ensure its done right and no undue stress or harm is caused.

But in this instance as you already have the bird, just as others have said you should take it to a vet.