So if all that value is gone now does that mean WhatsApp ceases to exist? Or does it have negative value now?
Today's price change means people expect to receive less dividends from FB in the future.
That cash flow can come from a variety of businesses within Meta, including WhatsApp.
It stands to reason that Facebook (as in the "facebook.com" component of Meta) is now regarded by these investors as being worth less than they thought before due to the fact that the company reported a decline in the number of users for the first time in its history.
It is also reasonable to ask what the more mercenary employees or would be employees of companies like Facebook do when stock becomes a lot less attractive.