Kane and Musiala will be the only players who have guaranteed spots next season and everyone else will be in trouble. I would say that Bayern will need to get younger, and the way to go will not be (obviously) selling of Musiala, he is already young enough, just 21 years old, and then he is going to end up playing for Bayern at least another decade.
Currently Musiala is projected as a player who can indeed replace Muller in Bayern's midfield and attack and with Kane there it could be a good combo just like Lewa and Muller have done at prime Bayern so it would be a shame if Musiala was released in the end.
At the moment the possibility is that he will be retained especially with the pressure from several clubs for the defense where Davies and Kimmich are also still not safe, so indeed Bayern must be extra in defending their current players.
It seems Nagelsmann's return to Bayern Munich is completely canceled and that's not possible anymore for Nagelsmann to be an option for Bayern Munich. Nagelsmann extended his contract and he is going to work at the German national team for a longer time.
However this won't be the reason to say Tuchel can stay in Bayern Munich for a long time because he even said himself and that he made his decision regardless of what Nagelsmann has done with the national team, Tuchel he is not going to stay in Bayern Munich in the next season and he wants to leave the team.