Speaking from a technical standpoint, if you want a good game which is something more than a kinetic novel and follows such model, you need a clever story with a lead heroine being the pivotal character in it. Someone, who's not only tied deeply with the events of the story, but also moves the story forward. That aside, the other girls' routes CANNOT act as "dead ends" for the story. They may be "what if's", but they CANNOT neglect, nor ingore the main heroine and whatever, that is happening in the background. All the events need to bo tied together, there can't be any lose ends; Side heroines and their routes should act as keys to solve the mysteries of the main route, or enchance/reinforce it, by giving the reader a possibility to look from a different perspective.
It's incredibly tricky to pull off and obviously, won't work with certain story types and genres. Majority of japanese scenario writers are godawful at what they do, there's no doubt about it. They often create events and introduce characters, which are either ditched or neglected afterwards; more like a one time fancy, rather than interesting plot mechanisms, which move the story forward. Aioku no Eustia is a perfect example of such writing.