Xabi Alonso's decision to stay at Leverkusen will make the Bundesliga even more interesting to watch next season. Xabi will try to strengthen his team and they already have good chemistry and a winning mentality. I'm sure Xabi will use the same squad as this season and will improvise some of their game tactics.
If Xabi improves Leverkusen squad and Bayern Munich hires a top coach, Bundesliga will be more interesting. But if Bayern Munich fails to hire a top coach, I doubt Bayern Munich will have the ability to compete with Leverkusen for the title next season. It will be nice if Xabi Alonso signs some top players to improve Leverkusen, he will prepare his team to compete in UCL, too. Anyway, I no doubt with Xabi's tactics, he is already proven it very well.
Munich will take revenge for their failure to win the title this season. I don't think they expected Leverkusen to be an unexpected variable and stop their dominance in the Bundesliga. They will certainly be better prepared next season and this will make the Bundesliga truly competitive.
Bayern Munich must try to take revenge. But if there is no change in the tactics and players' mentality, I am rather doubtful Bayern Munich will succeed to take revenge. Bayer Leverkusen is no longer an average team, they are a strong team. We can see it very clear that Leverkusen never gets a single lose until now. How Bayern Munich takes revenge with a such prefect team like this? Moreover, the current condition of Bayern Munich looks very unconvincingly. I also heard that some key players of Bayern Munich may be leaving for the next season. This is not good issue for Bayern Munich.