Dortmund's miscalculation clearly lies in their inability to show Rothe good enough prospects to make him stay for the current season. With the current changes that have been made to the Champions League format, alongside the already plentiful Bundesliga and DFB Pokal schedules ( and that doesn't even take Club World Cup into account), Dortmund could have found substantial minutes in an otherwise overworked and over-strained starting 11. Both Ryerson and Bensebaini, prior to their current injuries, had been played to their limit, especially considering the lack of minutes Kabar has been given and Couto's injury issues.
Rothe, on his end, has been excelling with Union, putting in some very impressive performances for the third-best defense in the league (8 goals conceded), only behind Bayern and Leipzig in this regard. His numbers per 90 (3.21 tackles, 2.2 blocks, 2.27 clearances) over the course of the last year, coupled with his two goals and one assist in the Bundesliga paint the picture of a player who has not only matured but is outright excelling in this step up to consistent top-tier competition. Rothe's performances have made many believe that he will likely also be a full-fledged German international in the not-so-distant future.
Rothe's performances bring into question whether Dortmund will look to exercise their right to bring Rothe back to the club.
According to SportBild, the way that the deal with Union was structured is that Dortmund has first refusal and the right to match any club that may wish to obtain Rothe's services until 2026. In 2026, the outright buyout clause (rumored to be somewhere between 12-18 million euros) comes into effect.