using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
        var rx = new Regex(@"(?<=^[^']*'([^']*'[^']*')*[^']*)\|", RegexOptions.Multiline);

		string text = @"1|'Nguyen Van| A'|'Nguyen Van A'|39
2|'Nguyen Van B'|'Nguyen| Van B'|39";

		string replaced = rx.Replace(text, string.Empty);
		
		Console.WriteLine(replaced);
    }
}