Earlier quoted context omitted.
How quickly is quickly? I've never had a CPU break on me, I still have laptops in storage a decade old that work fine, only they're too slow for the modern web. Perhaps 90C is reasonable for the time you will be using the device.
Individual transistors will break, the cpu will continue to work, but it will run slower. That's probably why your old laptops are "too slow for the modern web". " Some circuits and buses are protected by error correcting codes (ECC). If a transistor becomes marginal—meaning that it works most of the time, but occasionally fails—and thus only causes occasional glitches in those buses, then the processor may continue…
It is more likely that the thermal paste will degrade, the heatsink will get dusty, or things will start requiring missing GPU APIs, and fall back to software rendering.
Transistor efficiency also drops over time (creating more heat). Usually capacitors or connectors fail before that matters though.