Bayern Munich's mistakes are obvious and those mistakes may be why their team performance is so poor right now. Bayern munich changes manager and it is very common for them but this manager change has a bad effect on their club's performance which Bayern munich may not realize till now. Kompany may take charge of Bayern Munich again but how well he will do for the team is still a big question. But Bayern Munich must have faith in this manager and must give this manager time to fully implement his strategy and internalize his tactics. When the players understand a manager's strategy well, it will be seen that each player is doing well in his position, thus the team performance will be better and the team will have a chance to do well in the big tournaments.
Changing manager can affect the team and cause them some level of imbalance which I doubt if the team will be able to recover from almost immediately except after awhile before they will be able to probably get to recover from such. Some team gets Lucky that they get to witness good improvement immediately after they change their coach buy rhen it's not so common as most times it happens that the teams do suffer a while before they will be able to recover and get their form to the point they will be able to again some form of stability.
If Bayern Munich gets lucky enough, rhey may probably get to experience improvement by the tine season have gone half way already but this is actually under probability because their coach isn't a row quality coach buy an average coach who's probably trying such a big job for the first time. I believe kompany will be at his best buy my expectations from him are very low and not such that will be considered really high because I know he's not experienced enough with jobs as this.