After having issues on phones with WP 8.1, the app was completely removed without any promises of urgent fixes
After having broken down from the Windows Phone 8.1, Whatsapp has disappeared from the Windows Phone Store and has done so without promising any fixes soon enough. If the app is searched on Windows Phone, the phone simply displays the message reading that "We couldn't find a match. Try a different spelling or search term."
However, the app can be seen listed on the Windows Phone Store website but that is of no use since it comes with a warning that "This app is no longer published", and thus no option to remotely install it.
There is still some confusion as to why the app was completely removed from the store. It seemed to be working on Windows Phone 8 and only had issues with the updated Windows Phone 8.1. a possible explanation in this case might be that knowing that Windows Phone 8.1's release was imminent and that their app would offer a less than satisfactory experience as a result, WhatsApp opted to remove the app until they get it updated.
This also shows that the app might have had some serious bugs which couldn’t have been allowed to exist thus the app was entirely removed.
"Unfortunately due to technical issues, we have chosen to un-publish WhatsApp Messenger on the Windows Phone platform. We are working closely with Microsoft to resolve the issues and hope to return to the store shortly. We apologize to our users for the temporary inconvenience."