This is quite a tough thing, I rarely see Borussia Dortmund changing their coach in the middle of the season and with a very disappointing performance. Borussia Dortmund also should not be reckless in appointing a coach who will replace Sahin, because if they choose the wrong one then maybe they will be even worse. It is not easy actually when you have to be with a new coach in the middle of the season, because in terms of preparation, it will definitely be shorter and that is also a challenge. We can see Bayern Munich when they changed coaches at the end of the season, yes they couldn't do anything in the Champions League. But this situation is different, because at that time Bayern Munich's performance was still quite good.
It is a tough decision to make but I won't blame the management of Dortmund for their decision. The haven't kept a good record since the returned from the Christmas break and yet again they are losing in the Champions league when they know how much their fate relied on winning against Bologna which they ended up losing.
We never can tell what the future of this season holds for Dortmund. I just buy into the idea of a new coach so they club know and understand that they are just experimenting this season but if along the line the new coach is able to turn things around for the club then it is a big plus to them.