Correct me if im wrong, but the rules state "Damage dealt during the same action is usually dealt at different times since the dice are resolved one at a time . The only time multiple dice deal damage at the exact same time is when a die is being modified by another die"

Second Chance says "Before attached character would be defeated, instead heal 5 damage from it and discard this card from play"

Doesnt this technically mean you can kill a character twice with the same action if you did enough damage with separate dice?

example: Sabine has 1hp and Second Chance. I resolve 4 dice, which are 1damage, 3+1 damage, and a 2damage. Deals 1 damage, she "dies" but instead heals 5. Now i deal 3+1, shes back to 1hp, now i deal 2 and shes dead anyway.

i'm not seeing any thing that would halt the attack if the character died. Or for that matter preventing me from splitting my attacks up, long as i dont split the actual die

Correct.

The short answer is yes. It’s the same reason you can block damage with shields and Force Illusion during the same resolve dice step. You have the same rolls, target has 3 shields and force illusion. You resolve the 1, they take a shield. You resolve the 3+1, they force illusion. You resolve the 2, they burn the other shields.