I hope this doesn't edge to close to a 'What if' scenario as defined by the rules, but I often hear it said that the Cuban Missile Crisis could have caused an apocalyptic outcome if it went hot, a full scale nuclear war. But I've also heard it said that the ability of both countries to launch a full blown nuclear attack was more stymied than we often tend to think, especially since Nuclear missiles were still relatively uncommon and both sides were relying on bombers. The USA also had a significant advantage in terms of the number of nuclear weapons. How did military planners on both sides expect to approach a war if it was going to happen, and how did they think either country would fare from it? Was there an expectation of world ending destruction, as depicted in a movie like 1984's Threads or anything like that?
You should check out Robert S. Norris' "The Cuban Missile Crisis: Order of Battle." Norris, a well-respected nuclear analyst at the Federation of American Scientists, basically tallies up all of the nuclear forces of each side that were deployed during the Crisis.
It isn't a simulation. And to my knowledge no one has run one. But keep in mind that if the US was going to go to nuclear war, they were going to try to wipe out the Soviet Union — because they would be afraid of a conventional attack on European nations, and they'd be trying to mitigate Soviet nuclear forces against both their allies and against their homeland. And so those bombers that you have dismissed are going to be massively important: the Strategic Air Command's main thrust would have been waves of bombers against the USSR (and possibly China), loaded with thermonuclear weapons.
The Soviets definitely had fewer weapons than the US, and fewer capabilities for hitting targets in the US. They had a few dozen ICBMs operational during the Crisis, of unknown reliability. They also had some long-range bombers that would face considerable air defenses. So that's probably enough to do a lot of damage, but not enough to kill a nation as large as the US, especially if their missiles missed, failed to launch, or were destroyed by US/NATO forces before they could fuel and fire.
But they also had ample weapons for Europe and NATO powers, both as short-range missiles and bombers, as well as massed conventional forces, and would be seeking to blunt both the US/NATO attack against them, as well as taking as much territory as possible. And they did have some limited abilities to hit the US mainland.
My take take is that this translates into a totally destroyed Soviet Union, a totally destroyed Europe, potentially a partially destroyed Asia, and likely several major cities missing in the United States. And the fallout and potential climate effects of all of this would back up on the US as well in the long term.
This isn't what most people think of, because they're stuck in 1980s-versions of a US-Soviet conflict (by which point the arsenals were more comparable), and Americans rarely think about the European or Asian theaters, even though that was where quite a bit of the nuclear exchanges would probably take place.
In terms of how the planners thought they would fare it — the Soviets were under no illusion that this was one-sided and they would take a hard beating. They also knew that they had the power to seriously threaten countries that the US was allied with, and would do so.
The fact that the US might get away with only losing a city or two was the sort of thing that made generals think this might be "doable," but politicians blanched at this, for obvious reasons. Whether it would be "world-ending" depends on the world you're talking about, and how much credence you put into the environmental consequences of nuclear war, but it would be a slaughter unparalleled in history (US estimates of a full-on attack against the USSR around this time expected around 300 million dead, and that doesn't take into account counterattacks on US allies) and to imagine that things would continue "business as usual" afterwards is a folly that I don't think even the most hawkish really believed.