you could try this
spawn a civilian very far from the playing area (somewhere safe) and name him civ1
now in the trigger that turns the marker red, type also this in the on act
civ1 setdamage 1;
now for the trigger that ends the mission, type this in its condition
so when the marker turns red it will kill the civilian and the ending trigger will wait until he's dead from that condition and then it will activate.