Xavi will probably earn some money which he can use to transfer new players in their preparations for next season. Barcelona's performance has been much better than before but of course they still need some improvements, especially in defense and attack. Ansu Fati, Aubameyang, Ferran Torres are still reliable next season but Barcelona still need more players than just them.
Memphis Depay, Luuk De Jong and Adama Traure are unlikely to play again at Barcelona next season because they are rumored to be sold or returned to their respective teams. So of course Barcelona need a replacement especially Barcelona will be eyeing the title next season.
I actually think that Barcelona has a good enough forward lineup. the actual problem for Barcelona should be the defensive lineup. They don't have good defenders and that has cost them a lot of matches. Barcelona will have to think very closely about the transfers that they are going to make because play players who are going to leave Barcelona are surely going to leave some holes. And those holes need to be filled. But I believe first of all Barcelona should think about getting a good defender.
I do not understand the weakness of Barcelona's forward. I don't understand why Xavi wants to take a player like Lewandowski at the moment. Lewandowski is certainly a talented player. But we should not forget that he is 33 years old. He will not be able to serve the team for long. Moreover, the forward of Barcelona is strong. Xavi should spend money to stabilize his defense and midfield. If we don't strengthen the defense, Barcelona will face big problems next season.