I think there is a better chance that Putin's dictatorship will end before he dies of cancer. One possibility would be that the oligarchs, who are now separated from their money by the West, would rise up against him. Another possibility is that the Russian people will rise up against him; his invasion of Ukraine is immensely unpopular, and already, over 6700 people have been arrested by Putin's thugs for demonstrating against him. Another possibility could be that the soldiers, many of whom have relatives in Ukraine, might refuse to carry out Putin's orders of mass execution, which is undoubtedly the next step in Putin' siege warfare approach to the cities in Ukraine once they are surrounded. The massacre will be despicable but altogether possible, I'm afraid.
Waiting for nature to take its course, I believe, won't happen in time to save Ukraine if Putin's invasion proceeds according to his schedule.