Meanwhile, Xabi Alonso will definitely add depth to the squad to make it even better, if he succeeds in winning the treble winner then this plan will be easier to realize, because Leverkusen will get more bonuses. Xabi Alonso decision to stay could also influence the players decisions, I think most of their key players will choose to stay for at least one more season. By having better rotation options, Leverkusen can balance their performance in every competition they participate in, especially when playing in the Champions League and competing with other elite European teams.
If they want to maintain their performance next season then Leverkusen should try to add depth to their squad because they will be playing in the Champions League. The decision to stay is much better than leaving too quickly to take charge of another team because Xabi Alonso needs to prove his quality as a coach. Playing in the Champions League will mean that Xabi needs several quality players because the matches there will be much different from the Bundesliga.
I think the management will try to find a solution to add depth to the squad next season. Because they cannot possibly rely on a number of existing players next season because they are worried that if they experience injury problems, their plans to compete in a higher caste will be hampered by these problems.
I am sure Leverkusen will prepare themselves and their squad to undergo next season with the best competition. If Xabi Alonso stays for several seasons with them, then improvements can be expected for the better, but on the other hand Leverkusen will find it increasingly difficult to become the best if the current coach leaves for another team.
There are many rumors about Xabi Alonso's future at Leverkusen, as well as some of their best players. Some top teams will approach their good players and try to make a deal, so perhaps the performance of a team like Leverkusen will be difficult to predict next season.
By the way, Pep Guardiola seems to have started preparing the stamina of his best players ahead of the first leg against Real Madrid. I mean Pep Guardiola didn't play all his main players in the match against Aston Villa at the moment, so I see it as preparation so that the players don't get too tired for the next tough match.