I am not at home right now so forgive me that I can't recall card names, but here's the situation.
Ra, Argent Adept, Wraith, Tempest, Haka vs Ennead in the Realm of discord
Ra has the barrier in play and Wraith has the stance card, the villain draw was the "deal heroes 1, then deal them 1, then deal them 1" when we took damage we chose Ra to take it first, his barrier kicks in and damages the villain that was doing the damage, then Wraith took damage and did damage back to the villain. At this point the villain was KOed.
Now heres the question. Does the card continue to affect the other heroes or does it "fizzle" because the villain was KOed?
Yes, as Pydro said, if a thing is dealing damage and gets killed halfway through dealing said damage, it's no longer around in order to continue dealing damage. Another example for you is a game we had once which was epic fun - Ra, Expatriette, and someone (possibly Legacy - I think Expatriette was buffed from somewhere but not sure) versus Gloomy. Expatriette has Hairtrigger Reflexes. Ra has Flame Barrier. A Cultist (let's say, the Cursed Acolyte, because he hits everyone) comes into play and gets plinked by Expatriette. Then he attacks everyone...but we'll start with Ra. Ra's Flame Barrier goes off, finishing off the Cultist, who dies and comes back as a Zombie...which promptly gets insta-killed by Hairtrigger Reflexes (so Expatriette was definitely buffed, then, for it to have been at least two damage there...). Fun game :D.
Also, it works for hero stuff too - Visionary using Wrest the Mind on something is a good example - the Wrested target hits something, she redirects its damage elsewhere, then has to hit it and herself...but she hits it first, dealing enough damage to kill it, at which point Wrest is destroyed too so she doesn't have to hit herself because Wrest got destroyed before she could get that far :).
If it's the card I'm thinking of, it's been confirmed that with cards like that you deal all 3 types of damage to one person before moving onto the next. There's a similar card in Pike. So Ra would take all 3 damage then Wraith would take 1 and knock out the villain.
Ra wouldn't take three damage - he'd take six, this being the Ennead. Unless he has Flesh out, in which case I think only four since I seem to recall that one of the hits is fire damage.
The card in question is presumably Elemental Storm. From the card spoilers document:
The Villain Target with the lowest HP deals each Hero Target 1 Lightning Damage, 1 Fire Damage, and 1 Cold Damage.
I agree with the principle that actions can be interrupted. However, in this case, once whichever of the Ennead was lowest was killed, wouldn't the Elemental Storm continue, with the Ennead member that is now the lowest doing the damage?
My opinion: Once a source is determined, it doesn't change. That specific target deals this specific instance(s) of damage. If you open the door for the interpretation that the source can change, then would the new source have to deal each hero target damage? In other words, you could argue the new source has not dealt each hero target damage, and re-damage targets already hit by the first source. So for simplicitys sake, I'm on the side of sources not changing.
But Ronway is right. This has been discussed before and its currently up to players choice how they would like to handle this without a ruling from up high.
I guess that makes sense. Similarly, if a villain does 3+3 damage to the highest HP hero, that hero is determined and takes all the damage, even if she is no longer the highest after the first instance of damage.