For the next one or two seasons, Lewandowski still has the ability to play at a good level and he also still has a contract until 2026 with Barcelona, but what Lewandowski needs to do is avoid injury because when this happens it will stop his steps to play at a good level. His age is indeed not easy anymore, but being able to reach 42 goals this season is a very good achievement because not many players at that age can do like Lewandowski. Barcelona could use some young players when Lewandowski is injured so what needs to be done is to recruit lower players to strengthen the defense.
The difficulty for Lewandowski might be that it is becoming harder for him to compete with younger players, but so far he is been doing quite well. He was in excellent form before he got injured, so now he needs to be more careful, though it is easier said than done because anything can happen unexpectedly during a game. Ronaldo by his example shows that age is not always an obstacle to playing at a high level, and Lewandowski is still part of a top club. At the very least he will continue to play for another year at Barcelona, and after that he might receive an offer from Saudi Arabia if Barcelona decides not to extend his contract.
I think he will leave Barcelona after he gets fit for another year. Because Barcelona will definitely find a good alternative for him. Barcelona's squad is in very good shape and they finished last year magnificently. They were unlucky to be eliminated in the Champions League. As for Lewandowski, we can say that it was a good season in general. He will be 37 soon and his performance is magnificent for his age.