This is an archive related to a previous version of Esri Maps for IBM Cognos. If you need the current version go to http://doc.arcgis.com/en/maps-for-cognos/.
Any layer that you add to the map can be removed.
Once a layer has been removed, it can be readded to the map at any time. See Add IBM Cognos data to your map and Add data from ArcGIS.
The layer is removed from the map and is no longer listed in the Contents pane.