Recovering a deleted username
As long as you haven't deleted your entire Google Account, you may be able to regain use of your Gmail username by following these steps:
Sign in at https://www.google.com/accounts using the email address currently associated with your Google Account.
Note: If you deleted Gmail from your account, but didn't delete your entire account, you'll most likely still be able to sign in with what was your alternate email address (now your primary username). If you're not able to sign in with this email address, you may have deleted your entire account. In this case, you won't be able to recover your Gmail username.
While still signed in to your Google Account, visit the Gmail sign-up page and your old Gmail username will be pre-populated in the username field.
Complete the form, enter your existing Google Account password, and click Continue.
After you complete this process, you should be able to use Gmail again to send and receive emails.