Yes, it would be on topic. I don't see why this would be a worry.
On the other hand, if the VN does have the answer, I fear that people will end up downvoting the question for lack of research - "you'd know this if you played the VN".
you are right that the Visual Novel takes a while to complete and there are multiple routes. VNDB lists its length as
Very long (> 50 hours)
but I don't know if this is for getting all the endings.
There's also no official translation as such the only (and legal) way to get it in English is to buy the original Japanese game and download and install Amaterasu Translations's patch. Otherwise, if you can read Japanese you can skip the patch.
These 2 things can sometimes be a barrier to some fans who will instead stick to the anime, as such no one should be downvoting you for not having played the Visual Novel. This is like downvoting any anime question because you haven't read the manga it was based off from. A lot of the time (like Attack on Titan, One Piece, Naruto etc) it's because the anime is further back and not everyone has access to the manga legally (some people avoid the scanlations holding out for official localization).
Likewise downvoting a Studio Ghibli Film question for not having read the original book the movie is from which isn't a well-known fact, or Kantai Collection questions because you didn't play the browser-based game which accesses originally was based off a lottery.
Just because an anime is an adoption or was based on another media doesn't mean seeing that media is a requirement, so I wouldn't worry too much. Generally, if something would be a lack of research, you'd ideally get a comment explaining how you didn't do enough research and you can find out for sure or not if your question is happy answered or not.