Leverkusen will certainly have great difficulty repeating the same achievements as before. Competition in the Bundesliga is expected to increase after Bayern Munich and Dortmund start the new season, as well as other matches in Europe. Leverkusen will play in the Champions League, but they will probably be thrown into the Europa League if they fail in the group stages. They will never be the same even if Xavi Alonso will try his best, but still have a good chance.
I never think Leverkusen can match their unbeaten record next season, but everyone can expect logical things about them next season. Xabi Alonso has a big responsibility to maintain his team's performance, this is the most difficult challenge I imagine for him next season.
To be able to maintain the performance they have shown this season is a difficult task. The existing team will definitely change, whether it changes in a better direction or vice versa. I don't expect them to do that (maintain their unbeaten form), but at least they can give their best and still play well like this season. I am also sure that Xabi has prepared for this, he will also be aware of the difficult task they will face next season.
Maybe they can keep most of the players who brought them the success they achieved, and only bring in a few players who can make them even more solid. Because I see that the chemistry between them is very good, it could be a very good asset for them to navigate the next season. Their biggest challenge is in the Champions League, because they will face an even stronger team.