that's not entirely true. I forgot to plug the cpu fan in before on an xp2500+ and the bios shut down when the cpu overheated. cpu overheat protection is a standard feature of motherboards for many years. some athlon motherboard might not have it, but from what I remember most of the older processor run much cooler so a heatsink would be enough to protect it from complete failure. you would probably see some lockups or instability that would hint that something is wrong.