There isn’t an easy way to do this within the administrator – like many wordpress widget formats, if there is no content, the widget will not display. If you’d like to modify this behavior, alter your sidebar to check for content within the widget and display other content if none is found.
I figured out a solution. Just added an else statement to the widget function.
else {
echo $before_widget.$before_title.$instance['title'].$after_title;
echo '<p>No upcoming events</p>';
}