They're supposed to come back next year yes. And you didn't misread it, exactly; there are three tiers to that achievement and 50 Skulls is tier 2 while 100 skulls is tier 3.
news flash, you get skuls, you get items from skulls, and you would have to be killing like 1 boss an hour if you cannot get achievement in 2 weeks of holiday event.
Well i went to Stonefalls and went between a Dolmen and WB and got my 100 Skulls Chevo on Friday. What did i do next? I turned the game off and havent switched it back on as i have now realised that t
It's really not so bad; like hanging out at dolmens. Play with your collections, play with emotes, RP to the group (someone did that yesterday as folks were hanging out in a delve).