Ah, right. Easy to solve, but its not a condition of presence thing. You've got a trigger somewhere that is activated by the player being present, right?
OK. Make the trigger type switch.
Now, make your chopper waypoints look something like this (it doesn't really matter, its the principle that's important) The hold WP is far away.
HOLD <------- synchronise (F5) the trigger to this WP
DESTROY
DESTROY
You can use variables to achieve this, but there is no need. This is exactly what switch triggers were made for.