Klopp was seen in Dortmund training recently. It was really good to see him back there even though he wasn't there to coach. 
Klopp is very valuable for this team and the fans. He also knows that.
One day maybe he might be back to manage. However if Nuri Şahin is doing really good things there in that time then Klopp's team would be different. I don't think he would return to Liverpool after managing them for around 10 years.
But I would love to see him managing a German team again someday before his retirement. Because for now it doesn't seem like he has left his job for good.
That’s still a long way to go even though Jurgen Klopp is the one who coached Dortmund before he coached Liverpool. But I wouldn’t think it would be bad for Dortmund if the management chose Jurgen Klopp to coach Dortmund again even though it’s unlikely to happen anytime soon considering Nuri Şahin is the current Dortmund coach. And if Nuri Şahin can bring Dortmund to achieve better achievements, of course Dortmund will not let him go because any team will definitely consider that more than trying to replace the coach with a new one. Klopp is very valuable for this team and the fans. He also knows that.One day maybe he might be back to manage. However if Nuri Şahin is doing really good things there in that time then Klopp's team would be different. I don't think he would return to Liverpool after managing them for around 10 years.
But I would love to see him managing a German team again someday before his retirement. Because for now it doesn't seem like he has left his job for good.