No, you can count on that code work just fine. What you can't count on is your fetchList method working properly. If it throws an exception for any reason then that will not stop your program to tell you about it. The exception is captured and passed as the e.Error property to the RunWorkerCompleted event handler. You need to check it and take appropriate corrective actions, at a minimum let the user know.
You don't have a RunWorkerCompleted event handler. So of course you can't know why fetchList doesn't work.