Not sure if your code got clipped, but that doesn't look right.
First, register your sidebar in functions.php:
'name' => 'Default Sidebar',
'id' => 'sidebar-1',
'description' => 'This is the default sidebar.',
'before_widget' => '<div id="%1$s" class="widget %2$s">',
'after_widget' => '</div>',
'before_title' => '<h4 class="title">',
'after_title' => '</h4>',
Then you call the registered sidebar in sidebar.php:
<?php dynamic_sidebar( 'Default Sidebar' ); ?>
function_exists checks aren't needed; they're mainly used in themes being released for backwards compatibility when new features are added.
Once you have the code in the correct places, you should see the "Default Sidebar" on your Widgets screen in the admin panel. Then any sidebars you create with the plugin will override the default sidebar without having to make any additional changes to your code.
Let me know if that helps.