which is kinda similar to what happens in the Trickester stories in SJA, sure the character "committing suicide" is very clean, but the character does end his/her life to save the world.And hopefully a kid can see, or have explained to them, that by committing suicide she was trying to put history back on course.
of course the main difference is that they should already be dead, and have made a deal, but they still "die" to save the world.
never mind the fact that the kids regularly kill aliens, and dont seem to think much of it, killing a Siltheen is them like one of us stepping on a ant.