They were already moving, as soon as they saw the grenade had been rendered harmless, setting up, aiming, and firing their salvo of grenades through the small hole, to land perfectly between the targets, although, with Draiss' interference, that was hardly needed; the explosion of their ammo detonating is enough to cripple the heavy siege units, and the snipers don't make it far. However, before they make it very deep past this hold point, a warning signal goes off, throughout the base, and heavy bulkheads begin to close, sealing off both their retreat and their forward progress; even if Driass stops the ones he can see, there's likely more, deeper inside.