8 pin Hei problem

Unless you are running a 600hp monster I doubt it. Lots of us run HEI modules and they work pretty well. No idea at this point what might have caused the failure. Make sure the ground terminal is well connected, that it's mounted properly "flat" to the heat sink and that the charging system/ voltage is not going nuts.

It might also be that some coils (or a failing coil) is hard on the unit

HERE IS ONE THING FOR SURE: (that will kill modules) Something which allows secondary voltage to "shoot up" IE climb. Something which added a great deal of resistance or gap in the secondary circuit, such as a bad coil or plug wire, broken plug, or running it with a wire disconnected, or a rotor contact broken / bent