Please read below and use url links for details.
Disconnect channel from Google+
New channels created with a Google+ page or profile don't have an old username and can't disconnect Google+.
If you connected your channel to Google+ in the last 14 days, you can disconnect your channel from Google+ and switch back to your YouTube username:
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Google+ deletion or suspension
Once you link a YouTube channel with a Google+ profile or page, your YouTube channel is tied to the data of that particular profile or page. This means that deleting a Google+ profile or page will have a direct impact on any YouTube channel connected to it.
Your channel will be disabled.
Your comments and messages will be permanently deleted.
The following will be made private:
Your channel name
Your videos
Your playlists
Your subscribers
When you re-enable your channel, these items will be automatically restored. Note that subscribers may take up to a couple of days to restore.
You can't delete a Google+ page that's connected to a channel. You first have to delete the channel.
If your Google+ profile is suspended, you also won't be able to create new YouTube channels on your Google Account until you address the suspension on Google+.
Remember: YouTube and Google+ are services that depend on the existence of your Google Account. If you delete your Google Account all products and services attached to that account, including YouTube, will be deleted as well.
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Hope above answer will be helpful.