do I break a week of darkness to wish W and her Family Merry Christmas?

I was wrestling with that myself, especially since the ex had emailed me a 'merry christmas'. I think the answer is "yes". While I'm basically remaining dark regarding her, I concluded "friendship" means at minimum remembering birthdays and holidays, if you wish to keep a friendship going. But keep it simple! No sentiments, no messages, just the holiday greeting.

Being "dark" can have some shades of gray.