A new version of Azure AD Connect has been released with an interesting new feature: you can now re use existing AAD Connect database.
As you may know, the previous version did not allow you to re use existing database when deploying a new instance.
With the new version (1.1.614.0) you can now re use the existing database when deploying new instance to replace, if you need to move from a LocalDB to a SQL instance or if you need to restore your SQL instance. To know more about reusing existing DB go to https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnect-existing-database
You can download the new version http://go.microsoft.com/fwlink/?LinkId=615771