We know that a weave can be tied off to last forever (or as long as the One Power drives the Wheel), but we've also seen weaves specifically made to last forever start to fail due to the Dark One's touch. The main example would be wards against Shadowspawn and vermin that are placed throughout the Tower. It is clear from prior books that though the weaves were inspected, they were set in such a way that they were never supposed to fade. Yet the Dark One's touch causes them to weaken.

I am not quite convinced that saidin and saidar can accomplish the defeat of the Dark One because the Dark One has It's own power source that seems to be the equal of both to use against them.

I think the key lies in Rand's t'a'veren connection to Mat, Egwene, Nynaeve, Perrin, Elayne and other people.

Basically, I think he needs to direct his friends in the same way that Ishamael orders around the Forsaken as Nae'blis.