In this case, if a sender marks any media attachment such as photo, video e.t.c as a view once file, the file will disappear once the recipient opens it without been saved to the phone.
As I said earlier the main aim of this rollout is to enhance user control over their privacy.
Let's briefly take a look at some key characteristics of the new "View Once" feature
1. Viewed images, videos or attachments can only be viewed once by the recipient.
2. Viewed attachment won't be saved to the recipient gallery and as such can't be accessed twice except you resend.
3. You can't be able to forward, star, or save media's been sent via the view once feature
You'll be notified when a user opens the sent attachment
If the recipient doesn't open the chat 14days after the message has been sent then it will automatically disappear from the chat.
However, you will be able to restore the ‘View once media’ from backup if the message remains unread at the time of backup. If the photo or video has already been opened, the media will not be included in the backup and can’t be restored.

As I said earlier the main aim of this rollout is to enhance user control over their privacy.
Let's briefly take a look at some key characteristics of the new "View Once" feature
1. Viewed images, videos or attachments can only be viewed once by the recipient.
2. Viewed attachment won't be saved to the recipient gallery and as such can't be accessed twice except you resend.
3. You can't be able to forward, star, or save media's been sent via the view once feature
You'll be notified when a user opens the sent attachment
If the recipient doesn't open the chat 14days after the message has been sent then it will automatically disappear from the chat.
However, you will be able to restore the ‘View once media’ from backup if the message remains unread at the time of backup. If the photo or video has already been opened, the media will not be included in the backup and can’t be restored.
