Because of Star Wars Land, several rides are going down for a lengthy amount of time. Long enough that I'm not sure I've seen an end date. We know that Big Thunder Mountain area will be closed for good (Jamboree, Petting Zoo, Ranch, BBQ, but *not* the ride itself, or the rest Frontierland). For the extended time of building the new area, they have said that the following attractions will be out of commission: Pirates Lair on Tom Sawyer Island,
Disneyland Railroad, Fantasmic, the Mark Twain, the Columbia, and the canoes.
If I had to place my bets, I'd say they will be out all of 2016, and 2017, and possibly 2018. It took them 3 years from announcement to opening of Cars Land, and that was with an area that was already prepped to build (ie, not the extensive demolition that Big Thunder will succumb to). As I understand it, there's re-routing the river and trains as well, so this isn't just an "add-a-land" from the local amusement-park-superstore...