I’ve never replaced those and I have about 250K miles on a 18 year old car. I do replace spark plugs every so often. I’ve heard that if the o2 sensor goes it can screw up the catalytic converter very quickly.
If the cat WERE screwed up, would the car still run or would it also need to be replaced? If so, I would think that an o2 sensor would be kind of a maintenance item, ie spend regularly to avoid a huge expense if the converter goes. or maybe catalytic converters aren’t that expensive on this car?