At first, you will no longer be able to access your chat list. However, you will still be able to receive phone and video calls. Also, if you have your notifications on, you can still read and answer messages through the notification window or call back missed phone or video calls. After a few weeks of this limited functionality, you won’t be able to receive calls and the app will stop sending both messages and calls to your device.
But remember, once you delete your WhatsApp account, it cannot be reversed. It will erase your message history and remove you from all WhatsApp groups. And it will also delete your backups so make sure you’ve transferred that elsewhere before you delete.
Source: Android Community