OK, so Gavrilo Princip's gun misfires. That's pretty much the end of it. Consider:
- A thrown bomb was deflected into the street behind the archducal car by General Oskar Potiorek
- A few other would-be assassins lost their nerve and did nothing as the Archduke passed
- If I recall correctly, there was one other trigger man who attempted to fire but whose weapon (also) misfired; he took a cyanide capsule and jumped off a bridge--but the water was far too shallow and the capsule only made him puke. He was arrested, as you might expect.
- The Archduke got close to Princip only because of a wrong turn, compounded by the balkiness of pre-synchromesh manual transmissions of the day
Hence, for Princip to have a chance at all, a lot of things had to go wrong already. By that time, with the failed bomb, the Archduke was already pretty sore (to say the least), and the day would not be forgotten. So, if Princip's gun misfires, could well be that nobody even notices, or he'd get arrested also. That would add fuel to the fire compounding the already-ugly situation of the attempted bombing and the one would-be assassin whose weapon (also) failed. Seems to me that there would be some sort of move for reprisals against Serbia, but not war. Perhaps a sort of very rough analog to the Platt Amendment wherein Austria-Hungary could get involved in Serbian internal affairs when the situation apparently justified, like this; i.e., the Black Hand would be rounded up by Austrian officials and tried in an Austrian court on the grounds that the defendants were Serbian nationals who committed a crime on Austrian soil. The outcome of such a trial would be a foregone conclusion unless a Balkan Clarence Darrow were somehow to materialize for the defense.
In the long run, the result would be the same: Serbia would be a client state of Austria-Hungary, at least until Franz Ferdinand gains the throne. Then, the Magyars be damned (in his view), some manner of federalization would likely proceed, with quite possibly the lot of the south Slavs in the Empire being somewhat better economically than that of their brothers in Serbia or Montenegro. If not, and the south Slavs remain problematic, I could see those provinces getting expelled from the Empire. Serbia would probably absorb them, but they'd get problems along with more territory.
I don't really see a war resulting from this series of failed attempts. It took a while IOTL for Austria to decide on the military option even in the face of an assassination, so it's difficult to imagine even the most hard line anti-Slav officials gaining enough support for a war in this case. Long story short, I see:
- Some manner of federalism for A-H after Franz Ferdinand's accession, even with much bad grace by the Magyars (their alternative would be essentially a landlocked Hungary)
- Serbia as a long-term client state of A-H
- A Russian revolution triggered by non-military events (somehow, say, Rasputin's powers fail, the Tsarevitch dies, and the house of cards that is Nicholas II's reign collapses)
- No general European war in the first three, if not four, decades of the 20th Century: Russia would have to bounce back after the chaos of a revolution; the Balkans would have a sort-of-stability; Germany would probably liberalize after seeing changes in A-H and Russia
- Woodrow Wilson would serve two full terms and be recalled as a president who focused on domestic affairs, as well as one who set back race relations a good decade or more as well as one who promulgated the absurdity known as prohibition. Someone like Frank Lowden in 1920 would probably be able to overturn prohibition in the early 1920s since it was clearly a failure, and could probably undo a lot of the harm Wilson did in terms of race relations, especially if Harding were his VP
- The great northward migration of blacks from the south would be delayed by at least a decade or more until some sort of economic force majeure of an unknown sort happened.