Bayern Leverkusen will sell some key players, which will cause their performance to drop, and it will cause Xabi Alonso not to challenge for the Bundesliga title next season.
This is what happens when the smaller teams achieve success, it is very difficult for them to retain that level for a longer time, they surely lack the finances to better the team, and they also lose players and manager's to bigger clubs. Bayern Leverkusen will have no chance of replicating this next season, they will likely lose Xabi Alonso to either Liverpool or Bayern Munich, and even if Xabi stays, many big clubs will target their players and they will get some of them, which will weaken the team.
That's right, Leverkusen management will face a very dilemmatic situation in the transfer window, their coach and players will be targeted by big European clubs. It is very likely that Leverkusen will have difficulty repeating this season performance next season, especially if management cannot retain their coach and players. If only Xabi Alonso leaves, the next successor will not necessarily be able to surpass the unbeaten record that has been achieved at this time, so the key to Leverkusen future success is in the hands of the club management and officials.