I booked two bonus tkts to AMS in September 2012 for myself and my wife. For personal reasons we had to cancel and El Al put the tickets on hold for a year and we used them in August 2013. As far as I can remember there was no extra cost charged. Had we not utilised the tickets within 12 months I was told that the points would be refunded to my account (maybe this would have cost the $75 that others here have mentioned).
I am a PL, so there might be different rules for other members.