<?php
$s = '<div class="col">
  <div id="wrap">
    <div class="inner_wrap">
      Content 1
    </div>
    <div class="inner_wrap">
      Content 2
    </div>
    <p id="ab12">Hello</p>
    <img src="xy.jpg"/>
  </div>
  <p id="pqr123">Hello</p>
  <img src="ab.jpg"/>
</div>';

$doc = new DOMDocument();
$doc->loadHTML($s, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
$xpath = new DOMXPath($doc);
$nlist = $xpath->query("//div[@id='wrap']");

for($i=0; $i < $nlist->length; $i++) {
   $node = $nlist->item($i);
   for($j=0; $j < $node->childNodes->length; $j++) {
      $child = $node->childNodes->item($j);
      if ($child->nodeName != "#text") {
         $node->parentNode->appendChild($child);
      }
   }
   $node->parentNode->removeChild($node);
}

$doc->formatOutput = true;
$newHTML =  $doc->saveHTML();
echo $newHTML;
?>
