I get logged out a few seconds after I logged in to google plus video the popup when you click comments. I am then logged in to YouTube without the G+ intergration.
I use the self destruct cookie plugin, but it does not delete cookies that are in exceptions.
exceptions for cookies set are:
plus.google.com
accounts.google.com
apis.google.com
youtube.com
It works as long as I keep a Google plus tab open, as soon as I close it YouTube will log me out of the comments and G+ notifications.
Best Answer
The four exceptions I use are...
Just be sure, though, that if you run any type of browser cleaners (or cleaners that can clean out browser info as well as other stuff), disable the cleaner from cleaning site preferences; which is what these exceptions are. Otherwise, you'll have to add them again.