You're correct. If the sensor goes bad, it will think the engine is hot all the time. your fans will run the whole time the car is on, and it will do other things (like adjust the fuel mix) to try and bring down the engine temps.
generally you just replace these when they go bad. the ones on my car are the original ones- or are at least 4 years old, as that's how long I've had the car.
My old Maxima was another '93 and I owned it from 30,000 miles until it's death in 2001. never had any issues with the sensors in it being bad.