Lewa is still playing at a high level in Barcelona, but no one can predict what will happen next year. Maybe he is in his last year of performance, who knows. Maybe he can play in the Saudi Arabian Pro League for a year or two and earn his last money before he retires. Since he was so successful in Spain, I think he will be successful in the Saudi league as well.
Right now Robert Lawandoski is still quite impressive. He still has been doing so good, especially his finishing skill, which is still on the top shelf. So he can easily play 1 or 2 seasons before hanging up his boots, and that why I am in the favor of his staying. I mean, like, he needs to stay at Barcelona and spend one half season more with the great Catalan side. Because he is one of the best finishers in the world his presence makes some sense for the club, as well as his goals contribution, which is still appreciable, and that's why Hansi Flick has still made him a part of his team, although he is very old, but due to his goal-scoring ability, he has still maintained his position in the team.
So I think Robert Lewandowski should stay for one more season, and then after that he can retire from Barcelona if he wants, and if he doesn't want to then playing in Saudia Arabia will be better for him.