When the probes go on a thermometer, it becomes a useless device. Because of this, you want to ensure you take proper care of them to extend their lives as much as possible. Nothing lasts forever but there are a few tips you can follow to maximize their lifespan as much as possible. One handy trick is to wrap the probe wire, if one exists, with tin foil as this can shield it from flare-ups. Even though they will be heat-resistant, this extra precaution is not a bad idea.
Also, if a probe is not rated to be waterproof then you should avoid immersing it in water even when cleaning it. Instead, simply wash it with soap and water without actually submerging it in water.