personally, id rather have a functioning o2 sensor on my car at all times. But if you want to be a chode about it and tell him to drive it till it fails then so be it, just dont call me an idot for wanting new parts on my car and reccomending it to others to make sure its running at its peak. Afterall, changing them IS proper maintanence, do you change your spark plugs when they completely fail or when they have some miles on them??? im not about to use someone elses thread to start a arguement with someone elseIf your car is properly maintained they will last the life of the car. All sensors are made to last the life of the engine, usually poor maintanence and abuse ruins them first.
Never change a properly working O2 sensor. They are easily checked with the proper scan tool to see how efficient they are. Anyone that tells you they need to be changed at any time before failure is an idiot.