They take a long time, not just 1 year. Xabi at least took almost 3 years to walk. Xabi has consistently improved his performance. Therefore, he was rumored to be replacing Anceloti in Madrid. Because Anceloti has definitely trained Brazil. Xabi is a young coach who seems to have good progress.
The progress that has occurred while Xabi has been at Leverkusen has indeed made a lot of progress at the club. And this season is their best season in performance, in fact their performance is almost perfect. Currently, Leverkusen can be said to be a club that is very on fire and can also make changes in the Bundesliga over the dominance of Bayern. Yes, although we still don't know whether Bayern Munich will soon take over Leverkusen or not. because unfortunately, there are rumors that Xabi and Real Madrid have reached a personal agreement. but whether this will come true or not. If so, then of course this will have a big influence on Leverkusen.
If Xabi Alonso has reached a personal agreement with Real Madrid for me it is a very natural thing, because I think he really wants to be at Real Madrid. He's a former Real Madrid player, and I know he's a Real Madrid fan, so if there's an offer coming from Real Madrid he'll be very happy.
On the other hand, it's true what you say, if he leaves Leverkusen then it will have an effect, because we know that the person who brought Leverkusen to the current form is Xabi Alonso. Leverkusen will have to go back and look for a suitable coach who can replace Xabi and that will be very difficult.