2010-06-15
If the targeted creature is an illegal target by the time Vendetta resolves, the spell doesn't resolve. You won't lose life.
2010-06-15
If the targeted creature isn't destroyed due to umbra armor's effect, Vendetta continues to resolve. You lose life equal to the creature's current toughness (after the Aura with umbra armor has been destroyed).
2010-06-15
The destroyed creature's last existence on the battlefield is checked to determine its toughness.