If you want Xabi Alonso to prove himself for one more season in the Bundesliga, I think it will be difficult for Xabi Alonso to do that because Bayern Munich will not want any other clubs in the Bundesliga to beat them for the Bundesliga title next season. Secondly, 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.
I agree with you that next season will not be this favourable for Bayern Leverkusen and I have already observed that on my previous post because Bayern Munich has been the most favoured club that has been winning the Bundesliga but after watching there performance this season and seeing how Bayern Leverkusen has taking advantage of the opportunity to dominate the league they will make sure it never happens again next season, so even if Bayern Leverkusen was not able to sell any of there players before next season but I doubt if there performance will still be good as this season, although I no that predicting what will happen next season will seem a bit difficult but with the way the season is going there is every possibility of Bayern Munich taking back the trophy next season.