Sorry not having a go at you (you are just posting the scenario) but this thought experiment really just seems to be about getting to the end situation not justifying how it would happen realistically
No worries, I understand that you were criticising the TL itself and appreciate you making the effort to make it clear
If I may, I'll still precise a few points, as my previous post was a quick and imprecise summary.
The USSR almost certainly launch's at this point, why would they allow for tehri nuclear deterrent to be weakened / removed the whole point of MAD is the Nuclear detterrent must be maintained no matter what
The launchers that are being damaged during the conventional phase of the war are the medium-range SS-20, which iirc are dual-use. When reading the TL it did irk me a bit but, why not, it's WW3. I should have made it clear NATO does target ICBMs with conventional weapons.
This has been the ongoing goal for decades, there is no makeshifting this,
It's the wildest part of the TL
Giobatista imagined that during a conventional war all safety concerns would be put out the window and three different methods would be put to use; the first reasonable and the second, well, exotic but apparently proposed IRL. First, existing AA missiles such as the Nikes Hercules would be fitted with nuclear warheads, allowing for a "better than nothing" interception capability. Second, "nuclear mines" would be positioned in space disguised as satellites, to be detonated above launching ICBMs. Third, nukes would be buried in US soil and intentionally detonated upon reentry of Soviet nukes, so that the cloud of earth dust created would disrupt incoming nukes. I have to admit I didn't quite understand the latter two, but simply took the point that if peacetime concerns were forsaken a Soviet strike might be blunted.
I will add that Giobatista actually emphasised civil defense at least as much as those active measures. In fact, he envisions a significant share of both NATO and USSR population moving out of cities towards rural areas.
Why would the USSR do this, even in this scenario and ignoring the above points they are already in a conventional conflict with NATO?
It's one of the points in the story that made me raise an eyebrow as well. I suspect the real reason is that Giobatista needed political obstacles to a NATO first strike lifted, and the course of the war in China fits the bill nicely. Nonetheless, he makes an acceptable job of justifying it by showing how the Soviet leadership is trapped. After several months of fighting, the course of the conventionnal war is turning against them, so that they feel like they have to escalate. They debate between various forms of nuclear strikes directly against NATO, then opt for nuclear war against a non-NATO country as a convincing demonstration. Ample use of tactical nukes allow them to roll over the Chinese army (as well as author's fiat that the Chinese leader surrenders), but one of their cities is destroyed by a single Chinese ICBMs and they retaliate with anti-cities strikes.
That's it for me. If you are curious about that TL or want more detail, I encourage you to see the original thread - it also had its share of naysayers, and I must say the author attempted to engage with them thoughtfully and apparently retconned a couple of chapters on their advice