Oxygen sensors are not routine maintenance items and should not be replaced unless deemed necessary through proper diagnosis stemming from a check engine light or driveability concerns. There is no need to replace them after a certain mileage. My car has over 188,000 miles and my last car had over 240,000 miles on it and both used the original oxygen sensors which worked flawlessly. There is no typical failure mode of oxygen sensors. They can fail to switch altogether remaining at the bias voltage of 450 millivolts or can be slow to switch, be biased lean (low sensor voltage output) or biased rich (high sensor voltage output). the newer cars have a heated oxygen sensor which adds additional failure modes of loss of heater performance or loss of heater function altogether. Usually when a O2 sensor fails, the check engine light should come on if it is a hard failure. You can also get an intermittent check engine light if the sensor is malfunctioning and it only meets the diagnostic threshold periodically. The most common symptoms of a failed/failing O2 sensor will be fuel economy and/or lack of performance. If the sensor fails with a lean biased output, the car's fuel economy will suffer and you could see black smoke coming from the tailpipe. When the pcm sees the low output voltage, it commands the fuel mixture to go rich which means it's adding fuel. When the sensor fails with a high biased voltage, the car's performance will drop off. In this case, the pcm is trying to take away fuel from the mixture to lean it out.
