I feel like I should elaborate on my previous statement. Mage Wars really doesn't like simultaneous events. Even when things are meant to be simultaneous, they are handled mechanically in a sequential fashion.
Now, for Eye for an Eye, there's not really anything to say how the timing should be handled on it. I'm grasping at straws a little when I latch onto the fact that if the Defender is destroyed, Eye for an Eye still gets to do its damage. This is very unusual because Eye for an Eye should also be destroyed along with the defender, and things in the discard pile typically can't have an effect on the game. The one thing that this reminds me of is a Damage Barrier, which works in exactly the same way so as to convey the thematic feel of happening simultaneously with the triggering attack.
So, based on that information, I do think that Eye for an Eye is supposed to, in theory, be happening simultaneous with the triggering attack. However, that doesn't necessarily mean that mechanically it would be resolved simultaneously. In fact, after thinking about it, I'm pretty positive that it wouldn't be, because again the game hates to do that. Which basically means that I didn't contribute anything except confusion to the discussion in my previous statement. The only hard fact we have is that we don't know the timing. This will definitely be addressed in a future Supplement update.
I honestly think the final answer will be that the Defender suffers the damage and effects and then the attacker suffers the same damage and effects. I seriously doubt a ruling that allows the attacker to be damaged first, before the defender, will happen (as would be the case with any controller/initiative decides ruling), and it also seems unlikely that they would split up the damage and effects (i.e. defender takes damage, attacker takes damage, defender suffers effects, attacker suffers effects). Until an official answer is given, you can play it out however you wish, and if you have a good argument for another method then by all means share it with us, but right now I think that the order would be the Defender suffers the full damage and effects, and then the attacker suffers the same, which would prevent Vampiric from being beneficial to a fully healed attacker.