This happened just yesterday:
When the DM says, "The already unconscious paladin has his throat cut by the Darkling giving him 2 Death fails and now holds the blade to his throat threatening a final death slash if the party does not cease attacking."
The experienced players in the group stopped attacking, though some kept ranged weapons trained, spells readied, etc.. while they successfully negotiated their friend's release in exchange for allowing the remaining enemy combatants to simply walk away.
Whilst the new player in the group rushes in to attack causing the enemy to slash the throat of the comrade giving him a 3rd death fail and defacto character death.