@Override
    public void adminRemoved(Group group, Map<String, ?> params) {
        JID deletedUser = new JID((String) params.get("admin"));
        // Do nothing if the user is still a member
        if (group.getMembers().contains(deletedUser)) {
            return;
        }
        // Do nothing if the group is not being shown in group members' rosters
        if (!isSharedGroup(group)) {
            for (Group visibleGroup : getVisibleGroups(group)) {
                // Get the list of affected users
                Collection<JID> users = new HashSet<>(visibleGroup.getMembers());
                users.addAll(visibleGroup.getAdmins());
                groupUserDeleted(visibleGroup, users, deletedUser);
            }
        }
        else {
            groupUserDeleted(group, deletedUser);
        }
    }
Returns true if the specified Group may be seen by all users in the system. The decision
is made based on the group properties that are configurable through the Admin Console.

@param group the group to check if it may be seen by all users in the system.
@return true if the specified Group may be seen by all users in the system.
xmppserver/src/main/java/org/jivesoftware/openfire/roster/RosterManager.java