The help article [I accidentally created two accounts; how do I merge them?](https://superuser.com/help/merging-accounts) indicates:

> If you have two accounts that you would like to join together, please edit the ‘about me’ section of each profile to say “merge keep” and "merge delete" and then [contact us][1]. You will need to provide links to the two profiles you would like to merge - we'll merge the one you annotated "merge delete" into the one you annotated "merge keep".

> If you can't remember how to log into one of your accounts, [go here][2] and enter the email address you used to create it.

So, as long as you've used a valid email address for previous account, you might be able to recover it (and help speed up the merge process).

  [1]: https://superuser.com/contact
  [2]: https://superuser.com/users/account-recovery