I doubt if Leverkusen can continue to dominate after this season because bigger teams will come for their players and will lose a lot of key players and also they'd probably lose the brains behind their success Xabi Alonso. If that happens then they will surely go back to being the average team they used to be just has we've seen with many teams that pulled off similar stunt.
To guarantee a sustainable and productive team, the management and administration have to keep their best players and add good ones. In case they have excess, they could make a sell for a good price so they can improve further the team. That mistake was done by Borussia Dortmund when they let Haaland walk away without having a good remplacement and with injuries, the situation got worse.
Xabi Alonso are aware of this but my worries that he might leave the club to go to another one like Liverpool or Chelsea.