If Xabi Alonso leaves Bayer Leverkusen, then this will definitely be Bayer Leverkusen's final journey to become champions in the Bundesliga because the chance of winning will not happen a second time with a different coach. Xabi Alonso now knows the strengths and weaknesses of every player that Leverkusen has, so this coach is able to provide the right position for his players to bring victory. It is not certain that a new coach will be able to do what Xabi Alonso did.
Certainly Leverkusen will suffer the same fate as Napoli, where when Spalletti left Napoli, Napoli performance experienced quite a drastic decline. This could be exactly the same if Xabi Alonso leaves for another team then Leverkusen will lose their best form in the coming season. Xabi Alonso is indeed quite a genius coach because he managed to polish Leverkusen into the strongest team in the Bundesliga by being undefeated. There are many rumors that Xabi Alonso has a greater chance of coaching another team next season, so this season is of course his last season with Leverkusen.
But I still hope he can stay at Leverkusen because he is quite familiar with the situation at Leverkusen, where he already has a fairly good relationship with the Leverkusen management and the fans really hope he stays at Leverkusen for a long time. But in football everything can change suddenly, especially since Xabi Alonso is being looked at by an elite European team like Liverpool so it will be quite difficult for him in his current position. He can't possibly refuse it because he can build a better career if he trains a big team like Liverpool .
I agree with you and previously I had the same statement where the key to Leverkusen success is Xavi.
But what makes them so strong is the right positioning and strategy that is really mature and can be understood by all players quite well, this is one of the reasons why Leverkusen can continue to maintain its stable and consistent performance under coach Xabi.
There were many rumors that Xabi would become Real Madrid coach before, but it turns out that Real Madrid has extended contact with Ancelotti and of course this means that Xabi will be Leverkusen coach for longer, in the future he will continue with Leverkusen.
Everything will come back to what Xabi decision will be in the future because with Leverkusen he has succeeded in gaining big name and has really become great coach, I think it is impossible for him to leave Leverkusen so quickly.
Although many teams are interested in him such as Liverpool to replace Klopp, who has decided to quit at the end of the season.