Russia is an oligarchic republic.Even 10 years ago this was no longer true. Putin completely quashed the oligarchy -- and what he succeeded in building in its place has been by far the strongest one-man system the country has seen since Stalin. The oligarchy will likely have some success in reasserting itself, at least for a while after he croaks/fades in a few years.
His eventual successor will quite likely be another similar leader.
You almost want to wish, right?
The problem with the system he created is that it can only be managed by someone very much like himself. But Putin's really quite unusual, both for Russia and when compared with virtually any leader we've ever known anywhere.
His "successor" will likely be an effective power vacuum, visible to the outside world as an open-ended period of instability. It's entirely possible (likely even) that the security agencies will try to someone up the flagpole again, at least for a while. But it's difficult to imagine that person having the actual battery of intelligence, skills -- and sheer force of will -- to run things the way Putin has.
See also: Такого как Путин - https://www.youtube.com/watch?v=zk_VszbZa_s