Old vengeance type spell

Hey guys, long time no post.

I'm trying to make a spell that acts like the vengeance spell the warden had pre-tft beta. If a unit with the buff "Holy Illumination" dies, the unit who delivered the last blow will take 20 damage. In triggering this spell, i'm having troubles with the event/condition part of it. This is what I have:

Events:
Unit - A unit Dies

Conditions:
((Dying unit) has buff Holy Illumination) Equal to True

((Owner of (Dying unit)) is an ally of Player 1 (Red)) Equal to True

This doesn't set off the actions at all. I figure it's because a dead unit doesn't have any buffs. If this is the case, how should I go about doing this? If that's not the case, what's wrong? Thank you in advance.

The unit loses the buff when death.

You'd have to detect when the unit gets 0 hit points, but you would need to add that event to a trigger in game, this is where JASS is recomended since you can make it create a new trigger for the target unit and destroy the trigger whenever you need to.

You can keep adding that event for every unit in the map to the same trigger, Unfortunally , events take memory and they would leak