IOTL, when Konstantin Chernenko became leader of the Soviet Union in February 1984, he was suffering from multiple heart and lung ailments due to a lifetime of smoking. Consequently, he was only General Secretary for 13 months, most of them spent in hospital, before kicking the bucket.
Suppose Chernenko stays away from tobacco. As a result, when he becomes General Secretary in 1984, he's in good health-at least as good as someone his age can be. How long would he last, and what would the effects be on the Soviet Union and Cold War?