Up. I really wanna know this, as i wanna wait til the last day with buying the things i need, in case i get them in chests.
It'll most likely end at the first new build implemented after Halloween (this has been the norm in the past), but that means it's not a set date. Keep an eye on the test build forum and the announcement forum and you should be able to know when it's going to happen.
Plan on completing the Halloween content by the end of the 31st, we definitely won't remove it before, well, Halloween. And then there'll probably be at least a day's notice before a new build goes up but you should probably just buy everything by the 31st.
Speaking of which, are the Alyozo particular items going to disappear from the drop pool as well as the Halloween items? Specifically, will I still be able to find items like Spiritastrophe once the Halloween event is over?