Yes, reunification would economically benefit Mongolia, because it would make the unified country stronger. There are many very powerful countries in that part of the world. China and India are two of them. A unified Mongolia would allow the country to be more powerful and influential as they relate to the other big countries of the region.
Yes, a Mongolian reunification would benefit Mongolia economically, because it would allow the regions to work together. A unified administrative system and a compound economy would make the region stronger and less volatile. It would also make Mongolia more powerful against its neighbors, which are often very powerful. Mongolia would be stronger and more stable.