Orphaned entitlements groups can be created if all members can be deleted
Summary
Entitlements groups can be deleted and members of those groups can be removed as well. The member removal is not currently linked to the existence and viability of the group. Under these circumstances, an entitlements group can have all members and owners removed up to and including the state where the entitlements group has no members. At that time, the group becomes effectively invisible and unmanageable (though the system account remains a member, this is not exposed to end-users/admins).
Proposal
Upon delete request for the last member of a group, the operation should check to see if this is the last member, in which case the last member should not be allowed to be deleted and appropriate response code returned.