This scenario makes no sense. How would russian aircrafts with known nuclear capability cross so much NATO airspace without being taken down immediately? Also

This scenario makes no sense. How would russian aircrafts with known nuclear capability cross so much NATO airspace without being taken down immediately? Also, I don't think answering a single nuke with another nuke would be a smart move, especially when the radioactive fallout would hurt allies. Conventional destruction of nuclear and military capabilities seems a much more reasonable and efficient defense to me.