Summary

When an unmanaged user deleted the account, the account gets deactivated immediately. It stays in the deactivated state for the next 14 days before getting deleted permanently.

During these 14 days, the account can be reactivated whenever the user wants.

Reactivating the account

1. Go to id.atlassian.com.
2. Login using the email id account which is deactivated.
3. Enter the password.
4. In the next prompt, select Cancel Deletion.

That is it!

The account should be activated after this.