BuddyPress.org

This code will display the email addresses in the group members list:

<?php
$group_id = bp_get_current_group_id();
$user_id = get_current_user_id();
if ( groups_is_user_admin( $user_id, $group_id ) || groups_is_user_mod( $user_id, $group_id ) || current_user_can( 'manage_options' ) ) :
    $user_data = get_userdata( bp_get_group_member_id() ); ?>
    <div class="user_email">
	<label><?php echo $user_data->user_email; ?></label>
    </div>
    <?php
endif;

You’d need to overload the members.php for your BP theme and place this code in there.

To automatically remove their membership you could write a script to hook on the member role change and automatically remove them from the group but that’s a more complex job, you’d probably need to pay someone to write it specifically for your site.

I could probably write you a plugin to do that email me on venutius at buddyuser.com and we can talk about it.