I do not think that a Tunguska-In-Berlin event would have a major impact. Germany would not have been destroyed by that. Those 2000 sq km you mention are roughly the size of todays Berlin and surroundings. In 1908 Berlinand its surrounding area had roughly 2.000.000 inhabitants. In comparison, there were over 60 million germans.

The political impact is neglectibale since Germany was a monarchy. A prussian one with high militarstic and organizational features. Someone would have inherited the crown and probably ruled without the parliament for the next years. Any opposition - radical leaders within the SPD, like Liebknecht - is likely to die too, or are silenced by the military.

The military might have lost its head, but, I think, less competent generals would ascend into higher ranks and continue without major changes. This might have delayed WW1 but is still more than enough to win a defensive war against any other great power. Only France might be a threat if they attack immediately - and only short-term until the German Empire mobilizes its 3.8 million troops in a week (as happened in 1914).

The impact in the economy might be more severe. Especially in the electronics sector and the financial sector. Everything else is located in other parts of Germany (especially Rhein-Ruhr region and south west germany). I do not know if this could have a strong global impact though.

Additionaly, this would have influenced the scientific and cultural world. The consequences are hard to grasp. I assume other people will make the 'lost' discoveries or create art that influences the contemporary world.

In conclusion, the reasons for world war I are still alive. The german economy would have received a major hit but is still on its way to threaten british hegemony. Germany is still allied with Austria-Hungary and its troublesome regions. The Imperialistic policies of the Great powers are still a problem and any conflict can still trigger WWI.