Old question but maybe it helps someone else:
You could do something like this in page.php:
$postType = get_post_type();
if($postType == 'case_study'){
include('single-case_study.php');
} else{
// Do your page.php stuff
Old question but maybe it helps someone else:
You could do something like this in page.php:
$postType = get_post_type();
if($postType == 'case_study'){
include('single-case_study.php');
} else{
// Do your page.php stuff