look, lets just start with the basics because i have read this thread and i'd like to know where you get the idea that only the USSR and USA would just exchange nukes and that would be it. No, this is a war scenario. Any reason for launching the nukes would be to take out the opposition. Both the tactical and strategic use of nuclear weapons doesn't narrow the use down to just the major cities and the nuclear arsenal of the opposing nuclear power. If the attack is started, all will be started, not just the nuclear exchange. So, it will not be USA vs USSR but it will be NATO vs Warsaw pact and potential allies(like Australia for NATO and North Korea for Warsaw Pact). Believe me when i say nukes will fall on all those countires as well, but not in the first nuclear exchange, but once the war starts. Because nuclear war is not the exchange of nuclear weapons, it is also what comes after it, invasion. Don't you think they will go "Well we have used hundreds of nukes already, why not a couple more?" world has gone to shit anyway with most major cities in Europe, USA, USSR, Japan(definitely) and Canada gone, so if the enemy keeps resisting or starts executing their military war plans, one must do what you can to counter it, including the use of nukes. After the first nuclear exchange there will be plenty of nukes to go around, plenty of ways for delivery too. Nukes as a tactical weapon to destroy defenses and formations is an inevitability. The question is of course when will this war stop. There could be shock and awe at first, perhaps, but there are more nuclear powers, who knows how they'd respond?
bottomline is, so much destruction, will play havoc with the global ecology, killing more people than the initial blasts, fires and radiation.