Nah, we actually won titles
I would really like to know where people see the upcoming struggle? I mean, it is certainly not breaking news that Dortmund loses one star player per season to a European elite club. This started in 2011, when Sahin, the most central player who ever played under Klopp departed to Madrid. The next season we defended the league title and won the German cup on top of it. Then Kagawa, who lit the league on fire in his last 6 months, left. The following season we played one hell of a CL campaign and finished comfortably in the top3 of the Bundesliga. That was not good enough for Mario Götze, probably Dortmund´s best player since Andreas Möller in terms of raw ability, so he transfered to Munich. Result? Best season start in the club history, winning 14 out of 17 matches.
I know that people will now say that there is no guarantee that we will manage to compensate this in the future, but in football there are in general not much guarantees. It is more about probabilities. So, how high is the chance that the next (certainly) leaving player Lewandowski will cause major troubles or even a breakdown? The squad is way stronger and solid than three years ago. The financial possibilities are in a complete different dimension than three years ago (we made a profit of 50 Mil€ in the last season, whom the majority is still untouched) and we actually managed to creat some pull on the transfer market outside talents. We got the best player of a very impressive side, which managed to held their own vs. teams like Juventus or Chelsea last season, despite him having financially better offers from the Spurs and Liverpool. A top scorer from the Ligue 1 and one of the best defensive allrounders in the Bundesliga entered the competition for the starting spots there instead of playing as certain starters for other teams. All three of them named the same main reason for joining Dortmund: Jürgen Klopp.
He is the key figure behind Dortmund´s success and in difference to some players fiercely loyal to the club. Our success is less build on individual class, but more on our system and the collective team. It can´t be denied that we have some (mostly developed) highly skilled players (Reus, Lewandowski, Hummels, Gündogan,etc), but the truth is that the team is just as much carried by the unsung heroes (Großkreutz, Schmelzer, Bender, Subotic, etc.), who run their lungs out and produce consistent work rates that are unmatched in European football. This is the secret behind their movement and extreme fast transition football. They simply outrun the competition.
antohan asked what Dortmund can offer him in the future. We can not guarantee him to compete for the CL win every season or stay in the title race vs. Bayern Munich until the end of each season. What we can guarantee him is that he will continue to play under the coach who made him a star player. He was always a big talent but the size and speed of his development was unexpected and a very big factor for that was Klopp. Given that he is just 23 years old and far from finished in his development, he should stay at least for two more years and then transfer at his peak to a European elite club. I don´t expect him to do that, though.
Just like Sahin, Kagawa and Götze he will make the same mistake (the last one is an assumption on my part, but I believe it was not the right time for him) and jump on the first big chance to leave he gets, eventhough he is IMO not ready for that, yet.