It looks like Lewandowski will remain Barcelona mainstay next season even though he is getting older, his experience is really needed by Barcelona, which currently relies more on young players. He can still be relied on on the front lines even though his goal productivity has dropped drastically this season, Barcelona will not let Lewandowski go before finding a suitable replacement to fill his position.
Allowing Lewandowski to go this season will be a big gamble to Barcelona despite his old age. Players like him are good to serve as leaders during match and Ronaldo guide upcoming young players on how they can be coordinated in the field during normal and intense matches. Lewandowski's replacement should be found before he leaves and be allowed to play with him in the pitch in several matches in order to perfect the style of play of a striker. Real Madrid are doing the same and when the old player leaves, the younger ones don’t find it difficult to adapt again because of the experience they’ve accumulated from their predecessor. Lewandowski still has more to give to Barcelona, they should not even think of selling him for the next season to come also without having the best and most suitable replacement for him.
I agree that Barcelona shouldn't allow Lewandowski to leave soon, considering their financial situation. If Barcelona management allows Lewandowski to this season, they will need to sign another striker who can help them compete for the La Liga trophy next season. It would be better if Barcelona's management used the money to sign another player in another position that would help to strengthen Barcelona's squad. Lewandowski can still lead Barcelona to glory if Barcelona's performance is good. Lewandowski is a striker, and he can score more goals for Barcelona.