So he’s there until he dies you think?
I dunno. You can only make supposition based on the available facts.
You would need someone young, hungry and ruthless to topple him. But like a queen bee, Putin has proven adept at neutralising his rivals before they became a threat. Maybe he's smart enough to know when there's someone in a position to do to him what he's been doing to rivals for years, so he'll have a plan ready to jump ship. But for the time being he has too much support where it counts to be at risk.
Something drastic would have to change inside the Kremlin for his supporters to decide they'd had enough.
Those behind the scenes will only want to see Putin replaced by someone who will continue the status quo. Therefore you'll need more than simple popular support of the people to see Putin removed, and even then little will change in real terms. It will still be a corrupt hole.