Column sort not working

A bit dirtier working alternative I`ve come up with is:

add_action('pre_user_query','wpse_27518_pre_user_query');
function wpse_27518_pre_user_query($user_search) {
    global $wpdb,$current_screen;

    if ( 'users' != $current_screen->id )
        return;

    $vars = $user_search->query_vars;

    if('wp-last-login' == $vars['orderby'])
    {
        $user_search->query_from .= " INNER JOIN {$wpdb->usermeta} m1 ON {$wpdb->users}.ID=m1.user_id AND (m1.meta_key='wp-last-login')";
        $user_search->query_orderby = ' ORDER BY UPPER(m1.meta_value) '. $vars['order'];
    }
}

You can even schedule a daily automatic delete of unused accounts, specifying the max. days without login, like so (to be put in functions.php):

add_action('mydailyclearout', 'deleteinactiveusers');

function my_activation() {
if( !wp_next_scheduled( 'mydailyclearout' ) ) {
 wp_schedule_event(time(), 'daily', 'mydailyclearout');
 }
}

add_action('wp', 'my_activation');

function deleteinactiveusers() {
	  $days = 60; // days without login
	  $meta_value = time() - ($days * 24 * 60 * 60);
	  $user_query = new WP_User_Query(
	    array(
			'meta_key'       => 'wp-last-login',
			'meta_value'     => $meta_value,
			'meta_compare'   => '<',
			'meta_type'      => 'NUMERIC'
		    )
	     );

  	  $users = $user_query->results;
     if (!empty($users)){
	foreach( $users as $user ) {
	 if ($user->roles[0] =="subscriber"){	// only delete subscribers
          $user_email = stripslashes($user->user_email);
	  $user_name = $user->user_login;
	  $headers = array("Content-Type: text/html; charset=UTF-8");
	  wp_mail($user_email, $user_name . " unused account deleted",'Your unused account <strong>' . $user_name . '</strong> has been deleted.',$headers); // send an email notification
          wp_delete_user($user->ID); // delete the user
	 }
	}
       }

  $days=50; // you can even send a notification several days before for their consideration
	  $meta_value1 = time() - ($days * 24 * 60 * 60);
	  $meta_value2 = time() - (($days+1) * 24 * 60 * 60);
	  $user_query = new WP_User_Query(
	    array(
			'meta_key'       => 'wp-last-login',
			'meta_value'     => array($meta_value2,$meta_value1),
			'meta_compare'   => 'BETWEEN',
			'meta_type'      => 'NUMERIC'
		    )
	     );

  	  $users = $user_query->results;
     if (!empty($users)){
       foreach( $users as $user ) {
	 if ($user->roles[0] =="subscriber"){
	  $user_email = stripslashes($user->user_email);
	  $user_name = $user->user_login;
	  $headers = array("Content-Type: text/html; charset=UTF-8");
	  wp_mail($user_email, "Important! ". $user_name . " account is scheduled to be deleted",'More then ' . $days . ' have passed since your last login with <strong>' . $user_name . '</strong> username. If you dont login in several days your account will be deleted',$headers); // send notification email
	 }
       }
   }
}

I`m using this with success on my site, but for security you should test it out first on a nonproduction site first.
On a side note, this won`t list/delete those users to have never logged in or only before first plugin activation. For them you have to do the job manually.