If the sensor is bad on the bottom of the expansion tank you'd have to replace the whole tank.
I can't even find the sensor plug/connector on etka if you had to replace it for some reason.
I don't think the sensor burns out too often, I still have my OEM expansion tank on my 88 and the sensor still works. Unless you have a leak that you do not fix and it keeps tripping the sensor, wear and tear wise it just sits there until needed.