I love endings like the one you used, always have. It leaves everything open to imagination. While it does suck that there's not a part two (how could I not want one? I love all the characters and the story as a whole), I do still think it was the best choice to give a definitive "goodbye" instead of a "the end?" People are all too afraid to close the book. But if Niv wanted to continue, I don't think I would be opposed to that haha
I read a lot of visual novels, and I genuinely mean it when I say this is up there in one of the best, if not the best. I love each one of the characters, everyone is very 3 dimensional, and I absolutely love that you can make your main character be more you. Not just with pronouns, but also with the whole flashback idea, the ability to come up with a character that feels more yourself is absolutely wonderful, and I feel like it should be put into more games, definitely.
The only complaint I have with the vn is that it ended, that's all. It's perfect in every way and I think people need to take notes, especially when it comes to writing characters.