I think the whole forced rejoining thing will be solved via using the key to create permanent passages between the reflections, breaking down the barriers between the worlds equating making the world 'one' and thus nulling the need for the shards to rejoin destructively. Though currently our pathways are only seen/useable by us I believe this will change over the course of 8.0, after all the Milalla were able to use the key to mass exodus. In the hands of the WOL its true potential will be useable.