GDS has just updated but continues to only show SV123/124 flights, so, will be interesting to see what happens.
Today's Airline Route update states the Saudia flights for the winter are remaining as SV123/124 and at 3 weekly, but operating on Tue/Thu/Sat instead of Tue/Thu/Sun. Also the Thu service will be on a 2-class 772 from 18Dec - 31Jan. This matches what Saudia's own website is now showing, so seems to be the most likely outcome.