It seems the much-awaited ‘delete for everyone’ feature is not foolproof. The messages can be retrieved even after being deleted by the sender.
A Spanish tech blog has discovered a way to recover or see messages deleted by the other person in a WhatsApp chat. According to it, if an incoming message had generated a notification on the phone, it can be recovered from the notification log of the Android handset. However, this does not work if a notification was not generated, i.e., if you had kept the chat open or active when the message arrived.
There are two to three ways to see those messages. First, one can install Notification History application from Google Play Store. After installing, open the app and look for WhatsApp icon and you will be able to see those messages.
The second way is to enter the notification log manually. Long press on your home screen and select widgets. Scroll until you find settings widget. Pull that on your home screen. A new option will open with a slew of options to choose from, select Notification log. From now on, this setting widget will directly lead you to your notification history. After the notification log is opened, you can see all your notification there. Mind you, opening a notification here will load all the intricate details of that particular notification, not just the text.