I have a theory where the rest of the world goes on naturally. Because lets say there are no pegasi where the zebras live. Well who's going to make it rain? Well nature will. I believe, without pony intervention, the world will work the way ours does. But start manipulating nature for a certain amount of years, and now nature is dependent on you to change it. I believe there is a (for lack of a better word) "battle" between magic and nature. Both trying to dominate the other. But essentially, coming together so everything works out in the end. (Alicorns still raise the sun of course, same with the moon)