You are not that naive to think it's his murder that caused WWI, yes? It's well known that all sides had been preparing for world war.
Serbia accepted all parts of the AH ultimatum, except for one, which was a complete violation of sovereignty.
There were no significant negotiations over this, because that ultimatum was not intended to be accepted.
Germany and Russia and France and Italy all mobilized without all these things we hear today about new red lines and negotiations and compromises in Ukraine and elsewhere. Humans have not changed, it's just that war was certain to happen. The archduke's murder was not, but it was very convenient since he was a rather peacemaking figure.