Don,t panic,it always gets good snow from 10th Dec.You can almost set your watch by it.Look back at the webcam picture from christmas day last year.Enjoy your skiing.
there will be snow for Christmas, I hope U can still have fun in the clubs during the night, and if U are not a ski lover, U' ll have the chance to visit some interesting natural spots;
Ice rink
bowling in The Samokov
swimming in the hotel pools (mind the floor at the Rila as it is very slippery), looking around the shops
drinking and eating
chilling out
a trip to the Rila Monastary
a visit to Samokov or Sofia
Besides, even if theres no snow at the resort level, take a trip up the gondala to markoudjica pistes and there will be plenty, theres already been some up there and its not gunna melt. That's what i had to do last april when all the snow at the resort had melted. It's still a fairly large skiing area up there.
You can ski on a higher level thats true, there is snow it these days. If you have alook to the snow-forecast, you will see that the f/level is today a warm day around 2500m, so there is no rain can wash the snow away.
Or you even can make a trip to Melnik for a degusation of the best bulgarian wines, with a night there and on the way back visit the Rila Monastery, the most beautiful monastery in Bulgaria...