He didn't dare to make a move - things never ended, in situations like these, and even if he had risked putting away his gun in pre-won relief, it could trigger it all over again - but Vash wasn't exactly still. He watched, carefully, first Cloud's actions and then Luki's word, taking time to understand what it meant. Cloud was strong- the blade was stronger, sure, but the 'SOLDIER' had to be alright, or alright enough to last until Luki was for-sure calm. Had to be.
An uncertain impatience came over the Stampede right then, mind whirling, the part of his mind Knives had infected insisting he took the chance to disable the girl, to knock her out or make her run as planned- but he simply ignored that part.
And returned Cloud's wave with a slow-motion rotation of his own hand, frown finally relaxing slightly into that age old empty smile. Nothing jarring- just an alright, I'll wait for you, unless you think you're going to bleed out on that floor sort of gesture. Common practice, really. Expected, almost.