Probably not much. I’m sure it is in shock and in pain. If a baby, it might still be on it’s mom. If older, it is a wild creature and won’t do well in captivity. I doubt that you have the facilities for wildlife care. Trying to save it might be the wrong thing to do if most of its skin is ripped off. Your cat’s mouth is teeming with bacteria which will set up an infection in raw, open flesh. It needs antibiotics and stitches. Probably sedated too. If it’s injuries are severe, it probably will not survive.
Your cat is, by instinct, a hunter. The rabbit is it’s prey.