Liz from Google's YouTube support announced in a YouTube Help thread that they are removing the ability to reinstate a YouTube account soon.
We want to let you know that the ability to reopen your deleted account will be going away soon. The form will continue to exist for another 2 weeks during which time you will be able to reclaim a username that you previously deleted.
So if you need to reopen a deleted YouTube account, go over here before September 6th, 2011. If you do not, then the account will be gone forever.
Liz goes on to explain:
After this date, you will no longer be able to reinstate the username. In other words, once you've deleted your YouTube account, the username will become permanently unavailable.
If, after deleting your YouTube account, you want to have another YouTube account, you will not be able to reactivate your old YouTube username, you'll need to make a new account with a new username.
Please Note: Deleting an account is permanent, and you should not delete your Google Account or YouTube account unless you are sure you want to delete the account. Please see this help center article for additional information.