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If you keep a low temperature and no overclocking the cooler can last a long time.
How long? It is hard to tell, inadequate cooling and heavy overclocking will decrease the relative lifetime.
To avoid any overheating that can damage the unit I suggest to apply new thermal paste after a while of being used, clean the unit from dust, keep the unit up to date with drivers and BIOS.
To be honest is not that simple to tell what will be the lifespan of a unit. It all really depends on your specific unit. Let’s say we have 100 units of Intel® RTS2011LC. Then we would quickly discover that even though they all are the same model, they can be quite different in terms of performance and indeed the lifespan magnitude.