I've never thrown away a ticket on KE, but have twice on OZ. I simply called them up and told them that my schedule changed and I had to postpone my "return" trip, but didn't know the date yet. I imagine that there wouldn't be any problem to simply not show up, but being I fly them a lot didn't want any sort of negative marks on my record, if they even do such a thing. Another time they changed the "return" flight time earlier than when I'd purchased my ticket, and I informed them that my schedule didn't allow the earlier flight time, and they actually refunded me part of the ticket.