I did not quite get it. You saying, who should have died instead of Billy?
I say Lucas,, not because i hate him, he is an underrated character but because he could have died saving Max and Billy and El.
He would be:-
Protecting Max showing his love for her
Saving El showing how much he cared for her
Saving Billy showing that even though Billy disliked him and was racist to him, Lucas still did not want him to die. He knew how it would impact Max and after all, he was being controlled my the MF. He was an antagonist but still human.
No no no no, you don't understand. This post is like a ''What if''. If you could edit the scene, replacing another character with Billy, which one would you see then? Just an alternative scene, if you know?