The CPU failed, literally? Or the capacitors in the VRM circuit near it? Or a MOSFET near it? I guess the CPU could have failed it was really that hot (80*C+?). I find that dirty power and excess ripple from a power supply is more likely to kill the PCB of a hard drive than anything else (along with the capacitors on a motherboard, and RAM too) - physical faults of the platters more likely stem from extreme heat and temperature swings, along with excessive vibration.