Just because Leverkusen retained their manager and also most of their players by the looks of it, doesn't mean that they are going to be able to provide the same results. Sometimes you can keep everything exactly the same and you may still end up losing, we shouldn't really be worried about it.
I believe that the best thing to do would be just letting them do whatever they want, and I am sure that in the end they will do alright. Maybe they won't win the league, or maybe they won't win anything else, but I think it should be noted that we are talking about a situation that is going to be fine. I think it's clear, and we should be quite happy about it as well. Because we would be bored if one domination ends and another starts