You saw how quickly the blight was changing just after the last battle, while RJ confirmed shadowspawn die if the DO gets sealed away. So just going by the speed that was seen right after the fight, without the DO's influence it shouldn't take too long for the blight to be gone. Also will Rand share the growing song?
The interesting question will be what is done with all the land freed from the blight. We know Malkier is going to be reformed, but what of the other land? Will new nations arise or will the border nations expand?