I played this game a while back and the 19 separate parts made it very tedious to play and enjoy, that and the game engine. I noticed multiple people requesting this to be ported to renpy and others stating that the creator died so there's no way to access the games resources, but with a little research I found a tool that can extract all the sprites (images) and audio from the game called "UndertaleModTool". I personally wouldn't work on such a project as its a lot of work and I also question the legality of doing so, you'd probably have to ask for permission by the current owners of the game or something. But I thought it was interesting to find out it doesn't seem like a renpy port is impossible it is a large task though.