Users can create stand-alone content where they alone have the owner role, i.e. all administration rights. In case this user leaves the organization without inviting another owner for that blog / community / …, there will be no one left who may edit the members list or who may delete the feature. The blog / community / … can still be active though because all members and authors may create further content.
Solution with Websphere Commandline Interface
HCL does not provide a function to search for this kind of orphaned content.
Solution with Connections Administration Toolkit (CAT)
Navigate to Content And Access – Orphaned Content. Use the filter to search for orphans in the individual feature. You can look at the details of the feature, and then decide whether you want to delete it, or (in case of Activities and Communities with other features coming soon) whether to add additional members / owners.