Robert Lewandowski will soon be 35 years old and well as he gets older maybe his performance will also decrease. Because age still can't lie to the stamina of the players. We can see a decline in the performance of great players like CR7, Messi and Benzema as they get older. And Benzema is now going to an Arab club (Al-Ittihad) because he may realize that he is no longer young and it will be difficult for him to compete with young players who can still continue to improve from season to season. Like at Real Madrid last season, Benzema hasn't played much due to injury but a young player like Vinicius jr can replace him well.
I think so with Robert Lewandowski maybe this season he won't be as good as last season either. But if the 34-year-old player can consistently show his loyalty in Barcelona's attack then I will really appreciate it.
The decline in performance for a player like Lewandowski is very likely to occur slowly and not suddenly where when last season he was still quite productive by contributing 23 goals for Barcelona then suddenly this season his number of goals dropped to 50% it looks impossible because Lewandowski is one of the players who consistent, the season is about to start he will still probably score a lot of goals for Barcelona unless he gets injured but that rarely happens in his career, and I can't imagine if their main striker drops drastically it will bring Barça in such a bad state because other Barca forwards are not as productive as Lewan, but next season it is very possible for Barca to start looking for a replacement, because as he gets older it will be difficult for Lewandowski to play full time also with the tight schedule of matches that his club must play, because Barcelona will also play in competitions europe.
Of course moving to another league will also be experienced by the Barca striker, especially if there is a club that wants him like in the SPL or MLS.