When you either delete a relationship class manually (through right-clicking and deleting it in the project Catalog pane), or if you do it programmatically (through use of managment.Delete operation by way of the Geoprocessing tools in the sdk), the origin table remains in the Contents pane, but the destination table is removed. It still exists in the geodatabase, since I can navigate to it in the Catalog pane and re-add it by right clicking and selecting "Add to Current Map" or by dragging it over to the Contents pane from the Catalog pane.
Is this intended behavior? If so, why? How does one get around that? How can I delete a relationship class and still preserve both tables in the Contents pane?