Anyone who has been following the development of football for long time will definitely not be confident in Dortmund being able to beat Real Madrid, can see that there is no history of Real Madrid losing when they entered the UCL final and what more, Dortmund is also not team in very strong condition.
I will say again that several times Dortmund could reach the UCL final in the past with very good conditions and having many great players but they all failed and only ended up as runners-up, for now their condition is much worse than in the past so it is impossible to achieve victory and record new history.
If this failure was the main reason for Terzic dismissal then I would also say that it was very ambiguous decision, Dortmund is not necessarily able to become strong team with new coach, it will take time to see the changes.

In this way, it will be much easier for Dortmund to perform better because Terzic has all the experience that can be very useful in changing Dortmund performance, the only mistake is that the support given by Dortmund management to Terzic is never adequate.
Just look, when Dortmund starts to improve and has players who start to stand out with great skills, it won't be long before these players will be sold and Dortmund performance will start to decline again, this is the problem that always burdens Terzic and makes him look like failure.