And that guy was gone the moment he had an offer by a superior club on the table. You know what Klopp did in 2003, when he narrowly missed (one goal difference) going up to the Bundesliga with Mainz and had multiple offers by Bundesliga clubs? He stayed for another five (!) years. You know what he did in the last summer, when he was the top candidate for Chelsea and Real Madrid? He extended his already long contract, which is actually a pretty big deal for him, because he honors contracts more than most in this business. He did that at a time when the third player he turned into a super star left and the fourth was already certain to follow next summer.
If his frustration about losing key players should be the main reason for him to leave Dortmund, then why is he still there? This is hardly a new development and also nothing he did not expect. Why not simply move up in the food chain by joining an European elite club?
I can tell you the reason. Because he wants to turn Dortmund into an European elite club himself and is so emotionally invested in this club, that he is willing to take the hard road to archive that. This is his vision of his project Borussia Dortmund. A vision that was according to himself halfway done when they won the Double in 2012, a vision that became clearer when they reached the CL final last year, but ultimatively he is not finished yet.
There are two possible ways he will leave Dortmund. Either by archiving his expected goal or by realizing that he can´t take the club further. This time is not nowhere near here yet. This may be 2018, maybe later, but not sooner, because it would contradict a lot of things the man Jürgen Klopp stands for. A lot of people who bring up Klopp as United´s next coach only see the exceptional things he has done with Dortmund, but don´t bother to look at the person behind the success. Him abandoning Dortmund now would be extremely out of character for him. If he wanted to leave he simply would do so when his contract runs out. He would not do so after renewing his contract again and giving the supporters false hope with his speeches.
I´m certain that he will leave at one point, because I think he wants to have one more challenge in his career. Either as national coach or outside of Germany.