Check to see if the replica exists by using the REST endpoint - > http://my.site.com/arcgis/service/replicas (this methods is not documented, but gives you a list of replicas by replica id).
The next question might be: what happened to my replica?
HTH
Thanks Dirk.
Not sure if the link you provide is correct? I can't see the "service" on the list of child resources on rest endpoint.