One of the pictus cat's at our store got both of his sides eaten out by a small jag (the pictus slipped through the divider) and we managed to save him although both sides were showing the rib cage already. We added some salt and nicked named it sashimi fish and surprisingly it survived. So your cat having a minor bite like that is nothing. Salt with some good filtering will make a hasty recovery. Just keep any live foods away for a while.