Benzema has achieved success at club level while defending Real Madrid, his peak after Benzema led Real Madrid to win the UCL and La Liga last season. For his success in helping Real Madrid win several prestigious titles, Benzema won the Ballon d'or at a mature age as a footballer. This success is very difficult to achieve again, especially with the increasing age of Benzema and his condition which is often injured.
As you mentioned, Benzima has accomplished a lot in Real Madrid, but he cannot improve on his performance from last season.
He is not a young player who still has age on his side; he is almost close to retirement, I believe, because he is the type of player who likes to give younger players chances, which is why he was able to win his one and only Ballon d'or, which many people know is his one and only because he cannot win more.
Real Madrid is known as a club that has no tolerance for players who are already old, when a player is deemed unable to contribute anymore to the club, they will immediately sell him or let the player leave when his contract ends. Benzema will not forever be a mainstay of Real Madrid, now that he is 35 years old, Real Madrid has started to look for a replacement for Benzema. I think Benzema will be at Real Madrid as long as his contract remains, after that his time with Real Madrid will end.
I doubt Real Madrid will offer Benzima a new contract, and Benzima may retire from football early because he recently announced his retirement from the national team; perhaps his club retirement is near, or he may consider joining another club for more playing time, but Real Madrid will undoubtedly let Benzima go once his contract expires.