Left in limbo if she didn't do it.A) Why do you think she'd be left in limbo? The event would have ended the exact same way. The only difference would have been a few extra lines of dialogue between the MC and Maria where he tries and fails to talk her out of it, before finally resigning himself to going to try and watch over her.
B) I'd agree the impact would be lessened if the conversation included the MC saying "Maria, you're a half-elf", but I'm not suggesting that. I'm suggesting "Maybe we should listen to Hana" or "I thinks this is a terrible idea, Maria" or something equally vague. I don't think an option for people to express disagreement with her plan lessens the impact of her being forcefully taken from the MC at all. YMMV, of course.
Okay, yeah, having an option just to say that is not bad, then go with her anyway to show your support. That is a lot different from where this conversation started, him telling her no multiple times, and not going at all.
Would give you a again, but I ran out hours ago...