Earlier, I accidentally joined my modded world with a vanilla client. It completely removed everything I had, which gave me an idea that can save other people from this clumsy mistake. How about that when you save a world, it not only gets saved in the saves folder, but also in a new folder called "forgesaves". When you load up forge, in the single player menu there would be a button called "Forge Saves". When you click on it it will bring you to a list of all the worlds currently using forge. Then you could click on one to select it, and then click a restore button to replace the one in the saves folder. I hope you take the time to read and implenement this. It would really be great.