He should have known? How? "I'm worried about you, because you put your life below the life of others. So I put an illness onto you, that will weaken and eventually kill you, whenever you save somebody. I'm a genius. Either you die because you save other people, which is, what I actually want to prevent, or you finally give in and let people die, which spits onto who you really are and tortures you. You are save now. You're welcome." Robbing your hero of everything, so he is free ...to live out his final days as a hobo. Are we sure the demon king didn't curse him with mad cow disease, while he was passed out? And then he wants to end it with either MC's death or his own, because "it won't end any other way". So MC has to either die, so that Alan can sleep well, not worrieng about MC death, because he is dead, or Alan himself dies, because if he surwieves he won't stop? Does he believe MC is Batman and he is the Joker?
MC can save him, if he wants to, but somebody who is that blindly stupid might try to do the same thing or something else again. It's too bad, that they might be needed as allies in Ravi's story arc against her sister (I can see this going in that shitty direction.).... Man! This author makes the worst character redemption stories I've ever seen. A waste of precious manga pages.
You know what, MC? Keep them alive, but make sure to report and sue them. And make sure they don't cross your path again. Ever again. That one press guy, that owns you something! Tell him the story.