Just got this update from NS. Basically due to work on the line between Amsterdam Centraal and Schiphol for the next year from the 15th December 2013, there will be no direct NIGHT trains between Monday 0100 & Wednesday 0500. Thursday until Sunday is not affected.
Please note this only affects the hourly night trains. Outside of these times the normal timetable is in place. You will still be able to get from Centraal to Schiphol but there will be a replacement bus service from Sloterdijk which will add another 20 minutes to your journey.
Of course you can also take the N97 night bus from the Leidseplein area.