Is it possible to revive SunPatiens after they have gone unwatered for a few days over summer?

Try one good soaking with fresh water to see if any of them revive, keeping them away from direct sunlight– at least while they are being nursed back to health. If any of them make it, they should be well watered and well fed in partial sunlight, until they are fully healthy. It is more than likely, they will need to be repurchased.