I almost completely lost my channel because of this new demand of google/youtube to link accounts. This has been a complete nightmare. because I have a legacy account (created before may 2009), I was finally able to unassociate my channel with any google account and then had to re-associate the channel with an existing google account. But it was a nightmare to say the least.
for those of you with legacy accounts, you can follow the info below and I hope it helps for those who have gone through this.
Unlinking is only possible for legacy YouTube accounts created before May 2009. YouTube accounts created after May 2009 cannot be unlinked from the Google Account.
To unlink a legacy YouTube account from a Google Account, follow the steps below. Please note that you will be immediately asked to link to another Google Account.
Make sure you're signed out of all Google Accounts and visit this page: / my_account_unlink
Enter your YouTube username and your old YouTube password from before you linked to your Google Account, then enter the verification code.
Next, click Unlink My Accounts.
You'll need to re-link your YouTube account to another Google Account. You can link it to an existing Google Account that you own, or create a new one.
Each Google Account can only be linked to one YouTube account and vice versa; if a Google Account already has a linked YouTube account, you won't be able to link another one.