Sorry but the whole concept of Advent Calendars mean it'll be gone by Friday
Just save the puzzle pages onto your PC...
I have a suggestion for Serebii. You should make an archive or something with all of the previous advent calendars. I know its supposed to be seasonal but really, there are some awesome desktops and puzzles! It's a shame to make them and then just have them forgotten after the New Years. If you make an archive then people who find serebii.net in the future, or people who were gone on vacation and for various reasons, couldn't access the site during the advent period can still enjoy them! They are really cool, and I myself am also sad that I coudn't get this years downloads since I was one of the people on vacation (yes, for the entire month). If they are gone from your computer, then you might be able to salvage all the stuff from any members who are still around that have them. I would much appreciate it if this will be taken into consideration!