Dragonglass doesn't kill the White Walkers, just the wights. The White Walkers are invulnerable to fire, which they can extinguish. And the weapons of the White Walkers shatter all swords but those made of Valyrian steel. So although the Unsullied and the Dothraki and the dragons will tear through hundreds or thousands of the wights, the White Walkers will break up defenses so that the massively superior numbers of the wights will swamp the Unsullied and the Dothraki. The battle will hinge on the ability of the Valyrian steel wielders to break up the White Walker spearheading an attack, eventually getting the Night King himself. The Valyrian steel holders are Jon, Sam, Brienne, Jaime and Arya, whose Valyrian steel dagger is to be mounted as a spear head.
Something that didn't happen was walling shut the crypt so none of the dead Starks raised could attack from within.