ive done a mission like that, give it flying height etc, then dont do eject automaticaly make them have to do t manually, then if they dont get out they go back to the helis base etc...
give them a time limit say of 30 seconds coz ive done it with a full uh-60 within that time, so give them text as well to say jump etc.. so if u do it like that it should be fine.