The Bard level 10 utility power Word of Lifeddi states:
Immediate Reaction Close burst 20
Trigger: An enemy attack reduces an ally within 20 squares of you to 0 hit points or fewer
Target: The triggering ally in the burst
Effect: The target can spend a healing surge. In addition, the attacking enemy takes a -5 penalty to all defenses until the end of your next turn.
The glossary entry for Dying and Deathddi states:
Dying: When an adventurer’s hit points drop to 0 or fewer, he or she falls unconscious and is dying.
Does Word of Life, which is an immediate reaction (and takes place after the ally reaches 0 hit points) interrupt the act of dying and prevent the character from falling unconscious and falling prone?