If the target artifact, creature, or enchantment is an illegal target by the time Vraska's second ability resolves, the entire ability is countered. You won't get a Treasure. If, on the other hand, the target is a legal target but isn't destroyed (most likely because it has indestructible), you will get a Treasure.

For a player's life total to become 1, what actually happens is that the player loses the appropriate amount of life (or in some rare cases, gains the appropriate amount of life). For example, if the targeted player's life total is 4 when this ability resolves, that player loses 3 life. Other cards that interact with life loss will interact with this effect accordingly.