Mkhitaryan wants to leave this summer - at least he told the press he considers a move away from Dortmund. Contract expires in 2017, he refuses to extend it and he doesn't get younger. He is at the perfect age to go to a very big club. Gundogan will leave. Contract til 2017, too. Hummels and Aubameyang consider a move. Hummels contract expires soon as well. It is believed that Reus would seriously consider a move when the best players leave. There might be a chain reaction. But I think that Dortmund would block a move of Reus and Aubameyang, if Mkhitaryan, Hummels and Gundogan leave. For the latter three it is just a question whether they get some money now or let them go for free next year. It could be they at least force on of the three to stay one more year, to not loose too much quality in one window (e.g. Lewandowski). But it is definitely possible that there will be a last-minute contract extension of Mats Hummels, and there are chances to keep Mkhitaryan as well, while Gundogan seems to be gone for sure. Reus is a good friend of Gotze, so if Gundogan, Mkhitaryan and evntually Hummels go, a Gotze transfer might boost Dortmund's chances of keeping Reus (they of course can force him to stay anyway). Reus is a good friend of Aubameyang, who would probably also more likley stay if Reus stays and there is no quality loss in summer, so either no one leaving or if players like Mkhitaryan get replaced by a player like Reus. You see, nearly everything can happen in Dortmund in summer. The only thing which seems sure is Gundogan leaving. Mkhitaryan and Hummels could force a move as well, while Aubameyang and Reus would consider a move if all there congenius partners leave, but they would be then forced to stay by the Dortmund bosses and maybe might be more pleased again if Gotze joins that summer. Edit: Of course, as @Kanonkop mentionned, a Gotze move would be very contrversiallly looked at by Dortmund fans. The majority hasn't forgiven him and especially the hardcore fans do not want him to return. While the Dortmund bosses said they would like to buy him. But they are weighing up pros and cons and if Gotze could ever be accepted by Dortmund fans again.