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).
15-06-2010
wotc
The destroyed creature's last existence on the battlefield is checked to determine its toughness.
15-06-2010
wotc
If the targeted creature is an illegal target by the time Vendetta resolves, the spell doesn't resolve. You won't lose life.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.