First sign was the CPU temp at 80degC and the Corsair H80i water pump reported to be 0rpm.
Then the CPU temp reached and maintained 88degC , the speed reduced to 1800MHz or less, there was a lot of fan noise and everything was noticeably slower than usual.
Then, suddenly everything went quiet and monitor went black, power was still on and fans going but quietly.
Now, I get nothing when trying to power on, just the quiet fans.
I'm assuming the i7 6700K is completely toasted and I need a new CPU as well as cooling, is that correct?
Is there another possibility?
(Motherboard is Asus Z170 Deluxe.)
It’s possible your system realized your chip was too hot and shut itself down in an attempt to avoid damaging it. If your motherboard supports the feature. It sounds as if it might if it attempted to throttle your CPU when it became too hot (80C is generally considered the safe limit for CPUs). Let your components cool, install a new heat sink, and see if your CPU still works. I’d be willing to bet it’s okay.
@JHaub2 is probably correct. There are some processors with far lower Tjmax values (I saw a 9th gen processor with 80c Tjmax the other day) and the processor may be hitting its THERMTRIP temperature way sooner (at a way lower temperature) than we think. Still, as an Intel employee working on thermal-acoustic features, I THERMTRIPped processors many, many times (and sometimes on purpose) without ever having one die on me -- but I have seen motherboards die because of the heat coming off the processor (motherboard components often have far lower thermal thresholds for damage).