Pretty sure there are many players on Bayern that may Succeed him, but for me, the talent and skill of Robert Lewandowski is still there and the way he played right now is just phenomenal but he will eventually be replaced by the younger generation that is for sure, and right now in the Bayern Munich team they had Serge Gnarby that is on Quarantine and can not play at the moment, Thomas Muller Joshua Kimmich that is also on quarantine, and Leroy Sane,
In my opinion, Leipzig was really great last season, I don't know what happen but the player departure goes to show a lot of things, and there are certainly great players that have left Leipzig on the verge of their success, but maybe there are still chance for Leipzig to make it to the 2nd standing, as long as Dortmund is still in bad shape.
Muller is just a year younger than Lewandowski so I feel he might retire around the same time as Lewis so he's definitely not an ideal candidate. Tbh, no one has shown enough potential yet to be a goal hunter like Lewandowski. The only player I know with such potential is in Dortmund and that's Haaland. His contract with Dortmund expires in about 2 years and more potential players could spawn up in the near future too.
Maybe but maybe not, he could still play another season, prior to Lewandowski's retirement, and I could see many potential candidates in the Bayern Munich team that will be sprung to be a good candidate, but I guess they can not attain the greatness of Robert Lewandowski just yet, but speaking of Erling Haaland, the potential of being like Lewandowski it totally beyond, but Dortmund can not keep him in the team forever, so he might have a potential to go to Bayern or other clubs that could sustain his talent fee, but for now it is a good thing for Dortmund having Haaland, and right now they attain the 2nd standing in the 1st division.