Deterrence is fascinating. Ignoring whether Ukraine had the codes to activate their Soviet nukes, or the knowledge or materials to upkeep them till now, when would they use them, had they kept them? Probably not when Crimea was taken. Probably not when the Donbass was invaded. If Kyiv or other major population centres were overrun, then maybe. But at that point, why bother if the capital is lost? Deterrence has failed, and sure nuking Moscow helps other countries, but Kyiv is either occupied, or nuked in retaliation. Plus, we would've missed that amazing turnaround. A conventionally superior foe could salami slice their way to the capital, knowing that only the city about to fall, or nuclear launch sites under attack would elicit MAD.
I know Quora isn't a good source of information, but I was interested in the responses to this question of how Israel, another country with 2nd strike capability, would respond to a surprise nuclear attack. Some of them were surprisingly more level-headed than I expected, not that these are generals talking, with the emphasis on tending to the population, then attacking the perpetrators, over retaliating against civilians. It's funny, because their doctrine has 4 red lines that could lead to a response. One of them, the destruction of the Israeli Air Force, seems particularly aggressive.
