Upon winning the fight, the hero will make a flashy entrance - usually from a battlement where all can see him — and shout that the Big Bad is dead, and there is no reason to fight any more. All the combatants will pause mid-fight to watch him, and after his speech, the evil army will drop their weapons and admit defeat.
There's never a handy enemy field commander or second-in-command to take charge, or an enemy archer who takes a potshot at the unprotected hero. Evil seems to discourage initiative. This may be because your average hero will have gone through said second-in-command on the way to the Big Bad, hence removing any secondary unifying figure.
[...]
The U.S government has been guilty of this, killing off high-ranking members of drug cartels and terrorist organizations again, and again, and again, and again, and again, and again, and again.
The success rate of these incidents has varied. Sometimes it does the job, while in others it gives the group an extra incentive to hate America.