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.
Dortmund management must have considered carefully about changing the coaching chair, and indeed this decision was probably taken after evaluating Nuri Sahin performance since returning from the Christmas holidays, Nuri Sahin has shown no progress for the team at all, on the contrary his squad performance in the Bundesliga was very bad and yesterday defeat in the UCL was the peak.
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.
This is a gamble for Dortmund management this season, if they manage to get a suitable replacement, we will see them back on track, if not, Dortmund will sink even further.
I heard rumors that there are 3 new coaches being linked and one of them is Erik ten Hag, I don't think he is much better than Nuri Sahin, so if the management brings him in, I totally disagree.