Thats a good question really as for now we dont know if Lewandowski is leaving for now , but it looks like he will.
Maybe Mane is one of the players that can get the Top Scorer or some of the Dortmund Players like Haller or Karim Adeyemi.
They all have the skills for , another candidate is Patrick Schick from Leverkusen.
Those are my personal players predictions for the Top Scorer of the german league.
When I saw the question first thing that came into my mind was Sadio Mane. Sadio Mane will be a big name in the Bundesliga next season, I'm sure he's gonna have good numbers of goal if at all not the highest goal Scorer of the league. Lewandowski not leaving Bayern Munich is under probability but if does not leave, he will also make a name too because he has always been a talented player full of skills.
We know the greatness of Mane when he was at Liverpool and this clearly will give high expectations especially in terms of Mane's performance can still be good there.
Even though it is still very difficult for the top scorer when there is Lewandowski in the Bundesliga, Mane's name will still be lifted with some achievements in the Bundesliga next season, I think it can still be done for Mane.
Yes, you are right, for me Mane has a lot to offer and give, I hope that this season he makes one of the plays to which he has us accustomed, however it is as you say Lewa is one of the best, and for me he is the owner of the ballon d'or and not Messi at the time they were competing, so here it is a question of merit.