So, I've found in searches that hats are not saved after Winter Bash. (Noted that one has a feature request to have a "hat archive" - which I think is a good idea just to be able to see what was previously earned).
But one thing puzzles me. Multiple hats stated that they could be earned after Winter Bash was over. E.G. if a certain rep/vote was required, they could be earned if the post later got the required values. How can that occur when all the hats disappeared today? Or am I misunderstanding something?