Somehow, something happened that led to the Seanchan forgetting about it. Ideally, whatever Aviendha does to rectify the corruption of her people also leads to a reformation of the Seanchan.

It's not as if her vision is a guarantee. I'm assuming it is a potential future, not something immutable. For any of it to take place, Rand has to defeat the Shadow, there are no guarantees there, at least in theory.