Yes, the script continues to process after the call to
header('Location: http://google.com') if you don’t explicitly terminate it! I just tried this locally. I added test.php to a site in apache with these contents:
<?php header('Location: http://google.com'); error_log("WE MADE IT HERE SOMEHOW"); ?>
And checked my /var/log/apache2/error_log for this entry:
[Tue Feb 12 23:39:23 2013] [error] [client 127.0.0.1] WE MADE IT HERE SOMEHOW
Possibly surprising, but yes, it continues to execute if you don’t halt execution.