Bayern have to fill his place because of Lewandowski's willingness to leave. Ronaldo can still play ball at that level. I don't see it as a situation against Bayern's structure. What I would criticize is: Bayern Munich is a simple team in the champions league. And if they lose the star in their hand, they can't show any success. Winning the German league is no longer an achievement for Munich. Their goal should be the champions league. If they call themselves the big team.
Actually Robert Lewandowski still have talented and enough for Bayern Munich next season, but he has try to leave Bayern before his contract ended next year, how ever make Bayern need to find new central forward replace with position leaving by Lewandowski. But Cristiano Ronaldo not as criteria for Bayern Munich depending have been on 37 years old, better looking for with young player and have chance to play with Bayern Munich about 4 until 5 years later. Not any special achievement if success with Bundesliga or domestic league only because Bayern Munich try how get top level and achievement on Champion League after failed last year.
If Bayern Munich's only goal is to win the Champions League next season, they will want to have Ronaldo in the squad. And if they have long-term plans, they will definitely look for a young player to replace Lewandowski. However, if Lewandowski leaves Bayern Munich this season, the Munich management may offer to sign Ronaldo.