I don't know if the UFC would release him. I doubt there's anything in the contract that would pertain to this.If it's confirmed he fought a cheat AGAIN he absolutely has grounds to ask for that. Whether you think he's worth it or not is irrelevant, if ufc feels that way they can release him.
If he decides to quit the UFC, he would likely be quitting MMA. He's 42, so maybe it's for the best.