I read this first thing when I woke up this morning and thought I was having a nightmare. I really feel for you in this situation. I couple thoughts...
1) I've never met a dog that was chill enough to live in the house that would eat a snaked. They simply don't move fast enough. Unless you have hardware floor near your snake cage, something will be left on the carpet. If you have hardwood or the like, is there saliva all over somewhere near the cage from his licking up his mess?
2) I doubt the dog ate it. Follow the instructions above as best you can. Also, setup a small "hide" with a heat pad under it in the same room and leave it overnight should you not find him. More than one snake has been reacquired this way.
Best of luck.
Paul