I would expect it to be open. It's mostly the west side of the park (Adv. Land, Frontier Land, Critter country) that isn't open during EE.
Your in for a real treat though because after the recent refurb IASW is in the best shape I have seen it in since the 1960's. I never really thought much of the attraction before but with it being in such great form, it really is rather spectacular.
I think Walt would be proud.