What you need is an integer comparrison.
number of units within range of hook location = greater than 0 return true.
If boolean is false, create a warden knife 5 distance (or some small increment) away from last hook location in an angle facing the target, and then run the same boolean check. continue the loop and exit until either the boolean returns true, or after there is about 30-50 (however long you want the hook to go)loops.
IF the boolean returns true, you need to make another loop, deleting the knife graphics one at a time, and also moving the target back.
If the boolean returns false, you need to make another loops that ismply deletes the hook graphics one by one.
I havn't seen the trigger itself, but I assume they did something similar.