This might be considered more by Robert Lewandowski when his contract with Barcelona is over even though there are many other things that are still very open to happen to him in the future. Because as you said that at this time Robert Lewandowski is still very much needed by the Barcelona team because he can still help more young players to develop in the Barcelona team. And the choice to go to the Saudi Arabian League is actually very good for him before he really hangs up his boots from the world of football.
Robert Lewandowski can give his best for Barcelona before his contract ends and now his job is to focus on finishing the season with some much better achievements. Barcelona will not let go of Robert Lewandowski before his contract ends because his contribution is still needed enough to help the team achieve something that is expected and his presence can also provide a better front line. Regarding the future after his contract ends, it can be considered later, whether he plays in the Saudi Arabian League or not before entering retirement in football.