The only problem with the above approach, is that the event handler will still be there sucking a few cycles of computing power. To fully get rid of the event handler first give it a name:
myevent= unit addeventhandler ["event","result"]
to remove it, use the boolean as suggested by The real Armstrong, but instead of simply exiting, add the following line to delete the EH:
unit removeeventhandler ["event",myevent]
this should work for you.
-Grendel