using System;

using System.Linq;

using System.Xml.Linq;

​

public class Program

{

    public static void Main(string[] args)

    {

        const string xml = @"<p>

<li>

      <BibUnstructured>Some text</BibUnstructured>

    </li>

    <li>

      <BibUnstructured>another text</BibUnstructured>

    </li>

</p>";

​

        var doc = XDocument.Parse(xml);

​

        foreach (var book in doc.Descendants("BibUnstructured").ToList())

        {

            if (book.Nodes().Any())

            {

                book.ReplaceWith(book.Nodes());

            }

        }

​

        Console.WriteLine(doc);

    }

}

​

​

​