Yeah, that achievement will be written in the Bundesliga history and the Bayer Leverkusen archives!
Xabi Alonso and his players will make something that is rarely done all these years but let's not forget for how long the team did not lose any game too

It will be interesting to see whether Xabi Alonso will remain in charge next season or not and if Bayer Leverkusen could maintain this form for long time.
Their opponent in the next round are Union Berlin which should be feasible.
Xabi Alonso has confirmed that he is not leaving Bayer Leverkusen because he wants to keep on building on his success next season. Hopefully, the club will be able to make history by maintaining its no-loss status till the end of the season which will make them win the Bundesliga and Europa League. Union Berlin had a convincing win in the last game with FC Magdeburg. The game with Leverkusen will be tough because each team want to be the one to stop Leverkusen from making history.
If this season we can get two important titles from the Bundesliga and the Europa League then Xabi clearly deserves to be awarded as the best coach, plus if next season he wins another title then that is clear proof of Xabi greatness.
More big team will want him and he will also have much bigger salary cap.
Currently, I am sure he has made the list of the best coaches in Europe because of what he has achieved so far. This was why many too clubs were waiting for him to show interest in leaving Bayer Leverkusen so that they could immediately sign him. Having an unbeaten season will automatically qualify him for the award, however like you said winning the Bundesliga and the Europa makes him as the best candidate.