Barcelona will have to look for a replacement for Robert Lewandowski when he is in good form as he has aged enough and if Barcelona cannot find another suitable striker to replace him in his presence then their performance will suffer again. The way Robert Lewandowski is performing, maybe we will see him again for the next two or three seasons, but he won't be able to perform as well as he did before. Although he can score regularly now, the striker is not able to perform as well as he did when he was young, so his performance and pace will decrease as he ages. Instead of this player, Barcelona need to find a player who can contribute well for the club. In such a position, Barcelona may want to select young and talented players.
Look at Ronaldo who is 40 years old, I don't see him playing worse, the same with Lewandowski, he is in great shape and is having a great season. Barcelona have already extended his contract for one year until 2026, and I think they can extend it several more times. He will not get a big contract but I think it will not be a problem for him to extend it for a year. Lewandowski plays better with Flick than he played with Xavi, obviously the attitude of the coach to the player also matters.