Benzema can surely play for more years however I doubt he would be able to play like this in those years also. Because I don't remember Benzema playing this much awesome in the previous years too. Of course I don't mean that he was bad then. But this is like a career-high season for him. And I don't believe he can have a season like this anymore from now on. And when Mbappe comes, Benzema is very likely to be in the subs unless Real Madrid change their formation. Of course Mbappe will need to earn his place in the starting eleven but I don't think that it would take a very long time.
Benzema was playing good but he was hidden in the shadows of the other attackers, mainly CR7. Once he was given the full responsibility, he doesn't disappoint the team and the fans. Let's be reasonable, CR7 whether in Juve or ManU made the other players shining less unintentionally I would say.
Benzema is getting older sure but this year he made big things, if he can bring the CL title home, he will deserve the Ballon d'Or for sure!