Usually, when you delete a Google Account, all related Google Services are deleted at the same time. There was a long-standing bug with linked YouTube-Google Accounts. When you deleted your Google Account YouTube as a service was not deleted.
Your YouTube Account was tied to the Google Account. Since the Google Account was deleted, the Google Account and YouTube password became invalid. You were consequently unable sign into the YouTube Account. The bug caused the content in your YouTube Account still remained live for a while though.
We’ve fixed this bug, and now when you delete your Google Account the entire Google Account, and related services (YouTube included), will be deleted.
We’re also retro-actively deleting the YouTube Accounts which were impacted by the bug and which were not deleted at the same time when you deleted the Google Account. These YouTube Accounts were inaccessible but the videos were still live on the site. The bug has now been corrected and the YouTube Accounts and associated content have been deleted.
When you deleted your Google Account, the entire Account, plus the related services should be deleted:
Due to the bug though, the YouTube Account was not deleted and the YouTube Account remained live on the site.
Now that the bug is fixed, all Google services, including YouTube are deleted when you delete your Google Account: