What would have happened if Stalin had lived another year? Who would've likely been Stalin's successor?

Vyacheslav Mikhailovich Molotov - was the protege of Stalin who fell out of favor, but may have been "rehabilitated" in such a scenario you describe to lead what would have been a decimated inner-circle; the paranoia of the old man would have left few standing near his throne if he would have lived another decade and may have found him looking to very few "old" comrades for his inner-court.