I would expect both the decorations and the separate ticket Halloween parties to be there all October as they were this year. The decorations and holiday overlay at Haunted Mansion were up in mid-Sept. The Halloween fireworks were only shown during the party. -- Suzanne
The Haunted Mansion overlay typically goes up right after Labor Day, and then stays in place until after New Year's. General park Halloween decorations tend to start going up around the same time, or shortly thereafter.