As per the API documentation, the host cluster element "data_center id=" is both required at creation(exclamation in a triangle) as well as non-updatable(lock sign). Is it right to consider that, not only is this a required element, but it can't be changed and deleting(disassociation) is out of question?

We have a RHEVM environment, where one such host cluster was created initially being associated to a data center. Later someone changed something, that resulted in the specific host cluster having no "data_center" element on it. Could it be that the association was deleted, or that the data_center itself was deleted, but the system didn't honor referential integrity, that it was being referred by other objects?