WhatsApp is totally fine. Also, if it were gone, it would immediately be displaced by something else.

The features of 'WhatsApp' should be a standard or de facto standard, that comes with every plan globally.

WhatsApp only exists because Carrier incumbents are unwieldy and stupid - I worked with them for years, they're incapable of an ounce of innovation, and tried to control the entire mobile web.

If you're old enough, you'll might recall 10 cent WAP pages.

They fought desperately to control every inch, the iPhone broke their control, it would have been slow moving without Jobs breaking their hold, now Apple has a similar control, ableit much more capable.

They would not.

Plenty of options for chat apps where your account is essentially your phone number. People would quickly organize around one of the options.