If you permanently delete the Google account you use to access Pokémon GO, we will lose access to your Pokémon GO account.
Some users may be able to create a new Google accounts with the same email address* as the previously deleted account. However, they will not able to recover the progress from their deleted account. When users in this situation attempt to log into Pokémon GO, a brand new account is created.
If you have recently deleted your Google account, you may be able to recover it. Please visit the Google Account Help Center for more information.
If you are unable to recover your Google account using the process, you will not be able to restore your Pokémon GO account.
Why does this happen?
Pokémon GO only looks at your Google ID token (not your email address) when determining if there's an existing account in our system. If you delete your account and recreate it, you may be able to claim the same email address as before...but the Google ID token on the new account will be different than that of your original account. When a user logs in with their new account, Pokémon Go only sees the new ID token. Pokémon GO treats that as a new account.
*This issue applies to users that create a Google account using an external email address (not an @gmail.com addresses).