I think, Leverkusen will remain focused on the Champions League and the Bundesliga at the same time and I am quite sure if Alonso can optimize their squad to be able to face the tight schedule next season, indeed the Champions League has a different atmosphere from the European League, but when other surprise teams can be quite capable of doing it and going far in the Champions League, Why do you doubt Leverkusen will not be able to do it next season?
Many people think that Leverkusen is a very lucky team without losing for one season in the domestic league, even in the UEL, they only lost in the final, namely against Atalanta and that is also not a failure in my opinion, they are consistent, it's not because they are lucky. in fact, if they are lucky they only win a few times, but they are consistent from the start of the season to the end of the season maintaining their record of being an unbeatable team and strange people consider that to be luck and cannot be obtained next season.
If Xabi Alonso still maintains his style of play and also keeps some of his important players in the main squad of course there will be changes but still the mentality and style of play will not be much different from the previous season, I don't know but I guess it seems like people are not confident in their abilities Leverkusen in the next season will definitely equate the team with the Napoli team which we know in the domestic league. Napoli last season won the domestic league with good results but after the new season they played quite badly and people don't understand that Napoli lost their coach while Leverkusen keep hanging in there, I'm sure Leverkusen will be a difficult team in the UCL next season and also in the domestic league they will continue to play the same way.
I think the saying "success is hard, maintaining it is harder" applies very well in football. Leverkusen took everyone by storm and I am sure a lot of people and teams were surprised. It's like these surprise teams winning a title that nobody ever expected, but 99% of the time they can't maintain that level of success. Remember Leicester City when they won the Premier League.
Leverkusen will have a much harder time next season. Not that it wasn't hard to achieve what they achieved, but teams will be prepared differently next time. Especially the top teams in the Bundesliga like Bayern, Leipzig, Dortmund. But also in Europe.
But the level they played was so high that maintaining it is almost an unrealistic goal to begin with. Playing a wholes season with a single loss, which was the final in the Europa League, has never been done before by any team in Europe. That's why it wouldn't be realistic Leverkusen is the team that could repeat that when prime Barcelona couldn't even do that.