He's not healthy, but I have a TL where Stalin survives his stroke (link in my sig).
The problem with a healthy Stalin is that by the 1950s he suffered from a variety of aliments, including having suffered both a stroke and a heart attack, being an alcoholic, and atherosclerosis (a disease where the white blood cells line the artery walls, causing the walls to thicken and limited the flow of blood to the brain). The POD needed to change that is fairly early (maybe Stalin stops smoking in the 1930s for instance) that it would butterfly away the Doctors' Plot. In addition no atherosclerosis in particular would change Stalin's personality, since the mental issues associated with the disease seems to have made him more mercurial, forgetful (he sometimes talked about dead comrades like they were still alive), and irrational. Change that and you change a lot of things.