Back from my old overclocking days - its heat that kills life. And if you keep that under control (what ages is the heatpaste, replace it ever so often) i very much doubt you'll have any life issues from the cpu itself.

Bearings in fans, caps etc. are also stuff that you need to keep an eye on.

I just replaced a i5-660 thats been powered on since 2010 24/7, heatpaste was fucked so it crashed during heavy loads :)