This causes no problem for the performance of this script, because the browser get immediatlely from server the notification that the requested file doesn't exist.
The whole script hangs whereever the <script></script> is located.
External server is down
AJAX call hangs
The main page is displayed except of this part which is computed by the AJAX call.
This don't work in Internet Explorer 7 and don't result in an error or warning but in an empty page.