wp_update_post to set post IDs to drafts not working

Well in your for loop, I think you’re missing the $postcount variable… also there’s a typo at $idss[$i] …. should be $ids[i] based on what you’ve shown.

for ($i = 0; $i < $postcount; $i++) {
    wp_update_post(array('ID' => $ids[$i], 'post_status'   =>  'draft'));
}

That being said I’d just go with a foreach loop.

The mistake that you’re making is the 2nd line.

<?php 
  $post_ids = $wc_query->posts;

  foreach($post_ids as $post => $post_id) {
    echo $post_id;
  }
?>

Assuming that results in a nice list of ID’s, then I’d do the following:

 <?php 
  $post_ids = $wc_query->posts;

  foreach($post_ids as $post => $post_id) {
    echo $post_id;
    $arrPost = array( 'ID' => $post_id, 'post_status' => 'draft' );
    wp_update_post($arrPost);
  }
?>

I’m afraid this is the best I can do without being able to access the files.

Remember var_dump() is your friend!