Now that is the problem, if Xabi Alonso is willing to sign an agreement to go to Real Madrid then obviously I can't imagine how Leveskusen will fare in the Bundesliga while on the other hand they are in very good form this season. But on the other hand I don't think that's likely to happen, or that Xabi Alonso would be rash enough to consider it, and on the other hand there's no way he'd leave a team as successful as Leverkusen for the contribution he's made.
And also as we know with the increase in Leverkusen's performance which is very surprising in just a short time it makes a lot of praise coming to Xabi Alonso and indirectly it makes his career even more soaring. So the point is maybe Xabi Alonso will not decide to leave so quickly, after all he is also still quite new at Leverkusen but has been able to make this team experience dramatic changes, and also the management may not allow him to leave easily.
Even if that happens, it will be for next season and of course Xabi Alonso also wants his career to be much better by coming to a much bigger team, especially as the offer coming from the Real Madrid team will definitely be very difficult to refuse.
Xabi Alonso has indeed played a big role in improving the performance of the Leverkusen team, it is proven that after his arrival the team's performance has improved drastically and this indicates that Xabi Alonso is a good coach.
In my opinion, the possibility of Xabi Alonso leaving next season is very big, he is now in the spotlight of many top teams which makes it possible for Xabi Alonso to make his coaching career much more developed and that is possible for Xabi Alonso to do personally.
Yes, maybe it's too early to conclude about his departure now and it certainly won't be that soon because on the other hand, Leverkusen still really needs his presence to continue to help this team maintain its consistency in the competition, Bayern Munich will not give up on catching up and if there is any indication news that Xabi Alonso will be leaving in the near future then clearly that is good news for Tuchel's squad. The other thing is of course true as you said that it is very difficult to refuse an offer from a club as big as Real Madrid, it is a dream for most players and maybe also coaches to be able to be there and contribute there.
But the conclusion that we can reach now is that it is probably too early and it will not be so soon for Xabi Alonso to leave Leverkusen, who has been very good this season, to move to Real Madrid. So what is more likely is that as you said in the next few seasons his departure will occur when Xabi Alonso has made several careful considerations to choose which place is more promising to expand his career as an unconventional coach..