Bayern Leverkusen will definitely decline in performance since Xabi Alonso left and some important players left as well but they have also made some signings which should cover the vacuum of the players that left and again Eric Ten Hag is now their new coach so he will also employ his own strategy that will help the team so even if the may not be title contenders but they can finish in the top four positions and qualify for the Champions League games. They still have some quality players in the squad who was developed by Xabi Alonso, they will continue in same spirit they played with last season so i don't see them having much problem next season.