So,
The first time I beat the game I talked the Forsaken out of their plan and lived happily ever after. This time, for a change, I told Valeran I wanted to join the Forsaken. Obviously, I'll try that ending, but will I get a chance to reverse this decision later in the game and save the world? Otherwise I'd have to load the game and go through the Dragon Mountains, the Ashen Wastes, the Sunken Citadel and the Ark all over again.