Basically, I'm hoping for violent mutiny of nuclear forces in the event of a first-strike order. It feels very strange to wish that people on the other side of the world who I will never meet will just give up their lives/futures and those of their families and kill if necessary to prevent the first domino from falling.
[1] In 1983, Stanislav Petrov's early warning system showed a total of five inbound US nuclear missiles. He correctly assessed these to be false alarms, and disobeyed standing orders to trigger an immediate and compulsory nuclear counter-attack. https://en.wikipedia.org/wiki/1983_Soviet_nuclear_false_alar...
3.& 4. Would mean Russia's self annihilation and they won't go there.
It's no joke that nuclear powers are saber rattling ofc.
2. US warned that there will be catastrophic consequences if Russia used nuclear weapons. It's not clear what exactly do they mean. But it would be logical to suppose that this would indicate full scale NATO invasion.
3. In this case Russia military doctrine allows to use strategic nuclear weapon which is certainly will be used against USA, probably military targets first.
4. This is likely to trigger full scale nuclear response to Moscow and other major cities and consequent response from Russia. After initial strikes there will be armageddon plan which will destroy every big force on the planet just in case.
I don't think that this scenario is very probable, but there's clear path to the end of the world.
My only hope is that China would not allow #1 to happen and if China would decide to isolate Russia, it'll not last long economically.