Given that there are no filters in the theme that you could manipulate, this is a bit tougher but you can alter the logout URL in general with the logout_url
filter:
function hack_logout_url_wpse_193113($logout_url, $redirect) {
$logout_url = parse_url($logout_url);
if (!empty($logout_url['query'])) {
parse_str(html_entity_decode($logout_url['query']),$qry_str);
$qry_str['redirect_to'] = urlencode(home_url());
}
$logout_url['query'] = build_query($qry_str);
$ret="";
foreach ($logout_url as $k=>$v) {
switch ($k) {
case 'scheme':
$ret .= $v.'://';
break;
case 'host':
case 'query':
$ret .= $v;
break;
default :
$ret .= $v."https://wordpress.stackexchange.com/";
}
}
return $ret;
}
add_filter('logout_url','hack_logout_url_wpse_193113',10,2);
echo wp_logout_url(get_permalink());