Why not somebody else continue this VN? They can continue the story, put new music and maybe different art style. This could be the only way to continue this VN without the original creator.
For that, you better create your own visual novel and leave it in oblivion, apart he left it almost at the beginning, there is nothing to work with to continue it, not to mention the fact that the vn is still his even though he has been missing for more than a year
