Personally, I don't think we will see Leverkusen in the top 2 of the Bundesliga next season. Leverkusen lost the best coach in their history. At the same time, they sold a lot of players from the squad. With the new coach and players, it will take a long time for their performance to stabilize. It is very unlikely that Leverkusen will stabilize at the beginning of the season. I would even say that it will be very difficult for Leverkusen to stay in the top 4 of the table next season. Teams like Dortmund, Leipzig and Frankfurt are not weak at all.
Bayer Leverkusen doesn't seem like they have what it takes to succeed in the league next season because of the change in the team and their inability to retain some of their top players but having another manager is something that can also help them if Ten Hag will apply a formation that will help their performance and also think of signing new players that will help them I the team. The chances of the team finishing in the top4 depends on their performance, if they perform well they will finish among the top4 but if they perform poorly then they may not make the top4 list.