Hmm I mean the worst possible outcome for him is for him not to be able to kill the gun devil but narratively it would be stupid for him to not at least die fighting the gun devil. He has two years left that will definitely decrease before they get to their encounter with the gun devil. Hmm but he's going to definitely die. I'm going to put my dice on him saving dianji in a sacrifice and then dying it seems to match because that's what HIMENO did. And also is dramatic irony which does match up with what the future devil said.