[nenelan]

There's no "resetting" the list. When it gets a signal, that's over and done with. Us storing and manipulating variables is kind of like that list you are talking about.
We'll go back to my tests I was talking about.
So, say we start with a variable $placeholder = 0, we'll set this when the Event Handler mob spawns in EVENT_SPAWN. This will be what we are going to use to test our signals with.
Now, rather than using

if ($signal == 1) {

we will instead use

if (($placeholder + 1) == $signal) {
     $placeholder = $signal;
     ##Anything else we want done
}

And then in the false condition of that test, put whatever you would do to reset the event, as well as resetting $placeholder to 0. Depop mobs, repop mobs, heal mobs, etc.
So, as long as you give your critters the code to pass the signals of 1, 2, 3 on their death, this SHOULD handle it quite easily, and the rest is just mob manipulation.

Hopefully that helps!