There are some other caveats which mean WhatsApp chat fans should use this feature with a level of caution.
WhatsApp says that if a user doesn’t open WhatsApp in the seven day period, the message will disappear. However, the preview of the message might still be displayed in the notifications panel until WhatsApp is launched.
You should also be aware that if you reply to a disappearing message, the quoted text might remain in the chat after seven days.
If a user creates a backup before a message disappears, the disappearing message will be included in the backup.
Of course, it’s also possible for a recipient to Forward or take a screenshot of a disappearing message and save it before it disappears.
source: express.co.uk