I'm currently playing a Sabbat vampire following the Path of Blood in a VtM game. In our most recent session, I encountered and fought two Camarilla alastors who were hunting me for committing diablerie.
Before entering combat, I used the Burning Blade Thaumaturgy ritual to allow my sword to cause aggravated fire damage. By rolling well I was able to cripple one with my first attack, and then I used Celerity to perform another attack against the other. This time I rolled even better and dealt many more boxes of damage than his health chart could handle, and since it was all aggravated he instantly met his Final Death.
My group (myself included) couldn't decide whether the rules allowed me to commit diablerie on him since he was presumably decaying rapidly. They seem to imply the vampire needs to still be alive (as it talks about a struggle between the attacker and the victim), but fails to come right out and say it.
Can diablerie be performed on a vampire who has just met their Final Death? If so, how long after striking the deathblow does a diablerist have to drain the victim before his essence is lost?