I think it is not even because Bayern Leverkusen will be playing both in the UEFA Champions League and in the German Bundesliga this season that will make Bayern Leverkusen not be a threat for Bayern Munich next season, which will give Bayern Munich the opportunity to dominate the German Bundesliga next season, but because Vincent Kompany has built a good squad depth at Bayern Munich that's difficult for Bayern Leverkusen to compete with even though they are only playing in the German Bundesliga next season.
Leverkusen are not the only team playing in both competitions, if Leverkusen are not going to do well next season it is not a fault from the coach or because they had to stretch themselves playing two tough competitions but rather needing more time to ready the team that can drag the first position against Bayern Munich. Leverkusen let go some of their important players plus a new coach trying out new things makes them not a strong contender against Bayern.