In this case dropping out to a shell script command is probably not the best way of doing what you want. The "killall" command will yank the rug out from underneath the Finder, not allowing it to do things it would normally do when closing (like saving its preference files). Plus you are dropping out of AppleScript in order to do something that AppleScript is better able to do.
The better, and simpler solution is this line in AppleScript:
Code:
tell application "Finder" to quit