Print a node display mode in a tpl file
Are you trying to print full display mode + teaser mode under full display mode? You can always render any display mode directly using node_view as 


  node_view($node, $view_mode = 'full', $langcode = NULL)


or with your example:

switch ($view_mode) {
case 'full' :

//content for full view mode here

$rendered_teaser = render(node_view(node_load($nid), 'teaser'));
print $rendered_teaser;

...


I would also recommend breaking your display mode templates out into separate files to simplify management. If your full mode should be the same as your teaser then using this method you can always just symbolically link the files on your server.