Running d2r on laptop

Modern CPUs (and GPUs) have good protection against overheating, when temps get too high they will "throttle" meaning they simply clock themselves down.

So there is no substantial risk to toast your CPU, what might happen if it gets too hot is that you see performane dips due to the CPU limiting itself (and then it will stay at the highest temperature that its own internal limits dictate - which might be the temperature you currently see if it already clocked itself down).

There is also no guarantee such limiting will lead to an actual decrease in performance, given that the game's core is old and potentially not too optimized for modern hardware.

Edit: one tip that wasn't mentioned is to check the cooling system for dust and potentially clean it. The easiest way is to blow it through with a can of compressed air designed for that purpose, most computer stores should have it. Don't use the vacuum cleaner as it is less efficient and comes with a risk of ESD damage.