The company says, “If you haven’t accepted by then, WhatsApp will not delete your account. However, you won’t have full functionality of WhatsApp until you accept. For a short time, you’ll be able to receive calls and notifications, but won’t be able to read or send messages from the app.”
It’s interesting that they say “for a short time” because it leads to questions such as what will happen after an extended period of time if users still do not accept? Will the company eventually stop users from using the app entirely, or delete their account? That remains to be seen, but in the meantime it seems like users will have to either accept it or find a different app to use.