Rodinia would have existed from the Precambrian era, about 2 billion years ago, to around 85 million years ago when plate tectonics broke it apart. Continental breakup is usually a mantle plume's doing--hot rock from within the Earth softens up tectonic plates, which eventually split. This is how the land masses now known as Madagascar, India, Australia and Antarctica broke up and migrated to their current locations on the planet. As this took place and the Indian Ocean formed, small fragments located on the edges of the rupture zone broke off--this is how the Seychelles came to be. Mini-continent Mauritius just wasn't so lucky, and it slipped beneath the waves, disappearing with time.