Running OverWatch On my Mac, would the over-heating kill this machine?
Of course the wear on your machine is higher when operated at higher temperatures. But the MBPs have a carefully designed cooling system that should keep temperatures within safe limits. 

If the CPU or GPU actually do overheat, they will throttle and you will observe performance decrease. It certainly won't hurt to provide some additional airflow, e.g. by putting the MBP onto a stand like one of these so that air can flow underneath or even using a fan.