Instead of deleting your account automatically, WhatsApp has now chosen a new path to follow. If you fail to accept the new terms past May 15, 2021, some of the app's essential features will be locked, which includes messaging and making/receiving calls.
With that said, WhatsApp won't actually delete your account - as previously announced. Still, that outcome is always a possibility since WhatsApp reserves the right to delete accounts after 120 days of inactivity.
Can You Lose Your WhatsApp Account (If You Don't Accept the New Policy)?
Yes, you can lose access to your WhatsApp account unless you accept the new policy. Since some of the essential features of the app will become locked and inaccessible, this will force you to abandon your account. And after 120 days, WhatsApp will delete your account.
If you wish to delete your account manually, go to Settings > Account > Delete My Account. Keep in mind that all your data will vanish from WhatsApp's servers, and that includes your undelivered messages as well.