We replace dozens of cats every week. It's more common on newer cars. As far as gutting the cat on your dad's car the only concern I would have, other than the legal side, would be the possibility of the check engine light coming on. The purpose of the rear 02 sensor is to monitor cat efficiency. Without a cat on one side you'll probably end up with fuel trim/adaptation problems. If it's a nice car and you plan on keeping it I'd bite the bullet and fix it right. Just my two cents.