I dont think this is an issue in the first place. Different pieces of media aim to do different things. This game is not trying to be Fallout 3 or Dragon Age Origins. Nor should it try to imitate them. I think this game knows what it wants to be - it is a fun, lighthearted and heartwarming anime-esque harem romp and it executes that incredibly well. And I think that is more than enough. In terms of the 'sacrifice' if it will even be included, I think it will just be something quite cheesy like the mc sacrificing himself for the girls then magically getting revived or something. And there is nothing wrong with that - I think something like that fits the tone of the game perfectly fine.I don't think Caribdis has the stones to kill off any girl either (or even the MC)*, but man I would respect the hell out of him if he did.
The thing is, a 'sacrifice' in a game hits very, very differently from a sacrifice in any other media.
In a film/novel/comic you are watching the MC go about his journey. In the game, you ARE the MC. His choices are yours, and thus it becomes very easy to make the player feel forced or railroaded. While a sacrifice ending can make sense and be rather authentic in other media, in a game many players often end up feeling unfulfilled (I personally believe this tendency to self insert is why so many players are so sensitive toward any sort of male competition in their games).
For instance, in the game Mass Effect 3 which- quality issues aside -had a notoriously downer ending, many players were immensely disappointed for the lack of a simple 'happy' ending. Contrast that with Game of Thrones, which had a similar lack of polish, but was also critiqued for the lack of protagonists death and/or causalities.
I'm not sure how to resolve this issue. Frankly the best way I've seen it done would be Dragon Age 1 and Fallout 3 WITH the expansion pack that modifies the game to allow player choice in their sacrifice scenes. Players must feel the weight of their choices, but also be given real, meaningful options either way.
*Of course, that may be out of the scope of the AVN genre. Let's be honest, porn is the Hallmark channel level depth in terms of character and story. Even stories with the potential for more depth, such as this one typically avoid it (as seen here in the latest episode, where there absolutely NO consequences for Orion's choices or actions).
I dont think every game should try to be realistic or have downer routes. Sure some games may want to do that but I dont think this is the developer's vision at least for this specific game. So worrying about how to shoehorn darker routes into the game is like trying to fix a problem nobody has - not the developer since I doubt it is part of his vision nor a large majority of the playerbase.