I think they have confirmed that Martin has shared his intentions with them, and the general story is going to go down the same route as a result, but events may unfold differently and minor/supporting characters might be written out or ignored altogether (consider Lady Stoneheart, for instance).
Like qs I worry about what B&W will do now that there's nothing to really hold them back. On one hand I think they mostly made a good decision when they decided to cut away a lot of the tedious stories last season. I fucking hated Jorah and Tyrion's shared journey in the books. But the show-exclusive stuff that they gave us in return, like Jaime and Bronn's kidnapping quest or the Sansa/Ramsay rape-marriage, was pretty hamfisted and all around terrible. They don't strike me as particularly good storytellers.
