I don't doubt Xabi Alonso because what they got this season is the result of his hard work since last season, not just luck, so it is possible that this can continue or even get better.
The heavy pressure next season will definitely be from Bayern Munich who will grow even stronger to compete for the title and of course that will make the Bundesliga competition even more competitive.
I guess it will be cant getting better as they have played the whole season of the german league and its hard to top that.
Leverkusen have to proof themself now in the Champions League , but i think that they will be doing that.
Bayern Munich for sure have already the pressure and with the change of the Coach and few players leave it will be not easy.