Importantly, _Serbia_ wanted to cause a war that would pit Austria against Russia. One of the parts of https://www.amazon.com/Sleepwalkers-How-Europe-Went-1914/dp/... that struck me was the offhand mention that Serbia was the one country involved that accomplished all of its foreign policy goals as a result of WWI.

I suspect that even if the assassination had failed they would have kept trying other provocations at least until they provoked an Austria-Russia war.