When Putin dies things will get ugly. He's spent the last 20 years building a power structure where he holds all the keys. I doubt he has any kind of successor in mind, he seems himself as the only one capable of leading Russia.
The one to replace him will probably not have the same backing from the citizens nor the Kremlin itself. And although I hate to say it, Putin is quite intelligent, which is one of the factors that has enabled him to stay in power. His replacement may not be.
