Hide widget if user is logged in without plugin

If you’re comfortable changing the code where the widget is outputted you could use the is_user_logged_in() function. Something like this:

<div id="widget_area">
    <?php
        if ( is_user_logged_in() ) {
            // show nothing
        } else {
            dynamic_sidebar('widget_name');
        }
    ?>
</div>

The downside being that this is now hard coded and you might have to add this function in a few different files.

Steve