Man, this is one of the few times I think we see Baku genuinely mad/upset. Even as he won he had a very angered facial expression right up until the point he realized Marco survived. What a guy.
Killing a MC to make your audience feel something just to bring him back is a terminal trope.
How am I supposed to be invested in any danger MC's can face when even if I see someone die he could be just fine later.
It never stated that Marco really did die, when Kudakora said that "Even if there was a god, he wouldn't be able to resurrect that" he was implying to the state of Amako, not Marco.