There is has been a lot of talk over the last year or so about migrating Enterprise Vault data to various different destinations. Some of those destinations are things like network storage inside a customers environment, or to NetBackup storage (again inside a customers network). There has also been talk of migrating data to the cloud, but just the other day I spotted an interesting opposite article:
Enterprise Vault Data Migration from Secondary Cloud Storage back to a Primary Storage Location
This is in effect a de-migration article, one which can be used to assist you in bringing the data on-premise when it was previously moved to the cloud. It's an interesting read, and definitely worth taking into account if you are involved in such a project.