Sahin will definitely be a cause for worry to him, as he is one of his idols. Özil on the other hand is not perceived to be a failure at RM at all in Germany, but rather a huge success, regardless of how it ended. You repeatedly hear youngsters like Draxler talk about how "Özil developed into a world-class player at Madrid". Gündogan might think the same, but still, he's very close with Sahin, so that story will play a role.
As to why his decision is taking so long, I do believe it's simply because of the injury. He would definitely be in a better position to negotiate if he was fit and performing well on the pitch. Personally, I hope he stays at Dortmund and maybe, one day, ends up at Barca.