The CM party dates will either be 12/5 & 12/6 or 12/12 & 12/13 this year. Everyone wants to know when the parties will happen, but no one knows yet.
It's really not that bad, though - I was there for a limited time last year and the CM parties fell right during my trip. I just stayed at DL until closing or right before, and did other things on those nights. DCA stays open, DTD is open, all the hotels are open. It is only Disneyland itself that closes at 6 p.m. They still do the snow on Main Street and the tree lighting thing. They still do the fireworks. They still turn on the lights for IASW Holiday. The Castle still lights up in icicles. It's just that shortly after all of this happens the guests have to leave!
Last year we assumed the CM parties would fall on the earlier December days (which were 12/6 & 12/7), as usual, but around early November-ish, we discovered that the DLR entertainment calendar was showing 12/13 & 12/14 as closing at 6 p.m. We then found out that the CM parties had been moved to one week later than normal. I have no idea if that was a one-time fluke sort of think, or if they will stick with the later schedule this year.
If the CM's know when their holiday party is (and you would think they'd know by now!), they have not spilled the beans thus far!