Kobold Tunnelers - Does shifting as an immediate interrupt prevent damage by nullifying a hit?

Question

Encounter number 2 Worship in The Twisting Halls adventure - part of the Red Box set contains Kobold Tunnelers (minions) with the following ability:

Triggered Actions:
Narrow Escape At-Will Immediate Interrupt
Trigger: A close or an area attack hits or misses the Kobold
Effect: The Kobold rolls a saving throw. If it succeeds it shifts 3 squares.

Three cases came up, and for a new 4e DM, I felt uncertain of the correct rules - given that this is the red-box adventure, it'd be good to teach all new DMs the correct way to think about these things.

1. Magic Missile - as per other questions here, does not "Hit" so any Kobold minion on the other end of that spell is dead. No saving throw. Right?
2. Surprise - The party had a surprise round on two of the Kobolds, so I ruled that the interrupt didn't happen. With combat advantage, two more dead monsters. I'm not sure if this is right. Does surprise negate triggered effects? If not, the next sub-question applies:
3. I had no problem dealing with a attack missing, save == shift 3. The thing that had me unsure was when a party member hits (which would auto-kill the minion), and the kobold makes his saving throw in order to shift - does the hit fail (which spares the Kobold) or cancel the damage (which, would kill? a minion?)

Answer 1

1. Magic Missile^DDI is not affected. It is a Ranged attack, not a Close or Area attack
2. Surprised^DDI is a condition. One of its effects is that no actions can be taken by the surprised creatures. An Immediate Interrupt is a form of Immediate Action, so it cannot be taken while surprised.
3. The Immediate Interrupt^DDI invalidates the attack against the kobold (assuming the shift gets him out of range.

   An immediate interrupt lets you jump in when a certain trigger condition arises, acting before the trigger resolves. If an interrupt invalidates a triggering action, that action is lost. For example, an enemy makes a melee attack against you, but you use a power that lets you shift away as an immediate interrupt. If your enemy can no longer reach you, the enemy’s attack action is lost.

Answer 2

1. Narrow Escape only applies to Close and Area attacks (i.e. Close Blast 3 or Burst 2 within 10, etc.). So Magic Missile isn't affected, since it is a Ranged power.

2. Immediate Actions are allowed in a surprise round (Rules Compendium p. 191):

   During a surpise round (but not on its turn), the creature is can take an immediate action, as well as opportunity actions.

   But,

   If a creature is surprised, it can't take any actions, not even free actions, during the surprise round.

   So you're ruling that the kobolds couldn't use the Narrow Escape if they were surprised was correct.

3. Since Narrow Escape only applies for Close and Area attacks, their goal is to shift out of the area of effect and not be hit. They interrupt the Fireball or other area attack and jump out of the way just in the nick of time. That's why it's called Narrow Escape.