If you only look at it as pure loss, which would be wrong, WhatsApp (Facebook) most likely made a lot more money (and will continue to so) with the data, than they were fined.
Is WhatsApp still a separate company? The real reason WhatsApp exists is to provide Facebook a backdoor into people's contacts so they can infer their social graph. Whatever "revenue" WA earns is peanuts, the real value is the collected data.