You could set a variable to activate the extraction, and check for the value of that variable as a precondition for a waypoint. Synchronising waypoints is in my experience less reliable than using variables in MP games and is therefore a method that I will avoid at all times.
(1) Create a trigger with Opfor not present, but put into the on activation field:
helicopter_extraction = 1; publicVariable "helicopter_extraction";
(2) Place the helicopter with a move waypoint right on top with the following text in the condition field:
(helicopter_extraction == 1);
(3) Place the next waypoint for the helicopter on the extraction point.
statement is for MP purposes: this ensures that the newly set value of the variable helicopter_extraction
is broadcast to all connected machines, thereby ensuring that it will in this case be set to 1
for all players.