I doubt it was as simple or as far-fetched as some people insinuate but it's neither a surprise nor i think it will make that much of an impact, sure, it's sad and all, but Sana was the smallest member and didn't contribute that much to anything nor had very interesting dynamics with other members, neither is her story that interesting.
She isn't like Aloe, who was like a slap in the face for most of the western audience as they witnessed their first graduation, or Coco who's career burned down around her for months before finally going out in a blaze of glory that will never be forgotten, or even Rushia, who caused one of the biggest dramafests in the community and was then unceremoniously pruned from the lineup without even saying goodbye.
Sana to me is just unremarkable in all aspects, a quiet career and a quiet graduation, to be remembered only by the few fans she ever managed to get.