I didn't know when Winter Bash would end, so when my hat disappeared, I thought that the site would be closed, too. But it was still open, so I could add a new animated knitting to my answer. Will it be available, so I can knit a winter knitting in summer?
There is no hard date for when the Winter Bash site itself will go offline and become a redirect to the contests page like previous years. It's a good bet it will remain up for at least a month, and is usually just left alone until fall when we start thinking about the next event. The only important note is that there is no guarantee whatsoever for how long it will remain up. It can disappear at any time, without notice. Just enjoy it while it's available.