delete_blog hook is delete_blog - Suggested hook wp_uninitialize_site mercator.php

add_action('wp_uninitialize_site', __NAMESPACE__ . '\\clear_mappings_on_delete');

/**
* Clear mappings for a site when it's deleted
*
* @param obj $site Site object that is being deleted
*/
function clear_mappings_on_delete($site)
{
$mappings = Mapping::get_by_site($site->blog_id);

if (empty($mappings)) {
return;
}

foreach ($mappings as $mapping) {
$error = $mapping->delete();

if (is_wp_error($error)) {
$message = sprintf(
__('Unable to delete mapping %1$d for site %2$d', 'mercator'),
$mapping->get_id(),
$site_id
);
trigger_error($message, E_USER_WARNING);
}
}
}