What is the worst case with a Code po422

Worst case is probably a new cat. When was the last time you tuned it up? Misfires are a common cause of cats going bad. https://repairpal.com/obd-ii-code-p0422

Worst case scenario is you need a new catalytic converter. Which is most likely the case. But be sure to troubleshoot the problem before condemning the catalytic converter. Check the oxygen sensors, especially the downstream oxygen sensors, and the wiring going to them. Look for damaged wires and loose connections. If it is the catalytic converter make sure you read the emission control sticker under the hood to be sure you get the correct converter! You can save some money by putting a universal converter on there as long as it's compliant with the emission control system on your vehicle. I've had a universal converter on my 2000 Grand Prix since 2013 with no problems. Hope that helps! Jim

Well since I posted this the check engine light Went off should I still go get it checked out or go get a tune up??

Neither, if the vehicle is running ok. Did you recently fill up the gas tank or is the gas tank below the one quarter mark? If so, that's why the light went off. The computer will only run the diagnostics on the catalytic converter when the gas tank is between three quarters and one quarter full. Keep an eye on it for now. Hope that helps! Jim