Pevara and co. showed the way to use the BA once you've got them. Bind them with new oaths of obedience. Remove the restriction of using the One Power as a weapon, put them under the control of the Aes Sedai and you've got a force that is completely expendable, but highly deadly.

The Seanchan are defeated, but certainly aren't in a truce with the Aes Sedai or Rand. Having them kept alive as cannon fodder to go toe to toe with the Damane if/when they next appear would have been sensible.

Or if you really do want them dead, send with a couple of minders who can Travel to Tarwin's gap and move into the blight with them ordered to destroy all Shadowspawn encountered - the minders stand back and Travel away once they are all toast. Let their deaths hurt the Shadow twice over.

With a couple of minutes that's two viable options. Surely Egwene in her almighty brilliance (using what Verin and co. handed her on a platter), could have thought a step beyond 'BA evil, die die die now now now!'.