It's a widely held understanding that WWI was a foregone conclusion, and at the least, Germany was seeking a war. The assassination of Franz Ferdinand in itself was largely just a spark that justified the beginning of the war.

The most damning piece of evidence against Germany, is the December War Council. December 1912, German leaders decided that a war would come about in Europe, and determined that the best time for it to occur would be in 18 months (the summer of 1914), and that the most likely reason for its beginning would be a conflict in the Balkans (such as the death of the Archduke). Since the war did then begin in the summer of 1914, due to a conflict in the Balkans, and the fact that Germany gave austria-Hungary a "blank-cheque", effectively giving Austria-Hungary the go-ahead on whatever it wanted to do, it can be concluded that Germany wanted the war.

The Schlieffen plan also demanded quick German aggression, and so war would have had to happen at some point to break German encirclement. The day after Russia began mobilising its military, Germany declared war, and the day after they offered an ultimatum to France, Germany declared war. For Germany to avoid a war on two fronts (which they failed to prevent), they needed to quickly begin a general european war.

If the Archduke was not assassinated, a war would likely have sparked regardless, as there is a large amount of evidence pointing to the idea that Germany was seeking a general european war to break encirclement by 1914.

I'd just like to point out that this subject was also discussed in a recent thread, which gives a rather different perspective.