There is no full-proof way to know if the user has deleted their WhatsApp account, but some signs and symptoms can lead you towards some progress. Here're some indications that can be enough to verify if the user has deleted the account:

1. Messages Not Received
WhatsApp has a brilliant feature where the double tick next to a message indicates that the message is delivered to the receiver— and that's how you can find if someone still has a WhatsApp account or not. If a single gray tick appears next to the message and you don't get any reply, this can indicate that the user is no longer available on WhatsApp.

Note: This could also mean that the user has blocked you.

single tick whatsapp

2. Profile Picture is Blank
A profile picture indicates whether the person may have deleted the WhatsApp account or not. But you still cannot be 100% sure about it. A Blank or no profile picture can also result from that user's privacy settings.

no profile picture

3. Old Last Seen Info
Last seen is another way to verify whether the user is available on WhatsApp or has already deleted the account. An old last seen means that the person has not used WhatsApp since that date and time.

https://faqchat.ru/kak-uznat-chto-tebja … z-vatsapa/

Note: However, some WhatsApp mods can also fake that last seen (time and date), or the person might have hidden the last seen from the privacy settings.