Nonetheless, there is a continuous aging of the metal traces (electromigration) and especially of the insulating layers, e.g. the MOS transistor gates, due to the difusion of atoms.
This continuous aging is accelerated by steady-state high temperatures and it eventually results in either open circuits or short circuits somewhere, destroying the device.
Good MOS integrated circuits are designed for a lifetime at their maximum specified temperature of at least 10 years or even 20 years or more for the better of them.
Nevertheless, this is puny in comparison with the lifetime of many semiconductor components produced 40-50 years ago, before the continuous shrinking of the active device sizes, which could have lifetimes of hundreds of years, when free from fabrication defects.
I even think like you that my 45nm D510MO probably will outlive these! But it's so underpowered (like 1/10 of the perf. at 15W) compared to these that I'm willing to take the risk!
The risk of new boards being so much better that I'll have to throw these away ever is zero at this point, memory being the bottleneck!