I’d be shocked if Putin didn’t think about potential successors all the time. Someone in his position not only would have to plan for normal continuity of government, but identify and weaken threats, pit rivals and factions against each other, flatter and reward supporters, build legislative blocs, etc., all without spookung the herd. Putin has made himself indispensible to the ruling elite — there will be a mad scramble for power and spoils when he goes. Things will not get instantly better from our perspective.
Putin is that paranoid.