As YetAnotherNick said, logout might be the better word to describe the impact here (plus, a fairly aggressive inactivity deletion period).

I agree with you in principle, but I still don’t understand how else to mitigate this: WhatsApp must get a lot of cases of stolen unprotected phones. The victim can ask their operator to lock the SIM card, but their WhatsApp account would still be out in the open.

With the continuous improvements in mobile OS security defaults, I’d expect this scenario to become less and less of a problem, but it must still be accounted for.

The process still goes through support ticketing, so I’d expect a spike to be noticed and stopped.