See, even Batman is willing to go past the No Kill rule regarding Darkseid, as he is a cosmic evil. Darkseid even retorts aloud that "if the amazon or the kryptonian had issued the threat, he would have ignored it, but Bruce is a human, and humans are willing to kill themselves and their world to claim a victory; something Darkseid wouldn't ever do" (paraphrasing a bit). And Batman was wearing a combination of Apokolips armor and a motherbox in the comics, so it was a bit more "believable" for him to survive. He still gets almost punched to death.