How can I make the chat boxes disappear and disable the friend list on Google+ but not on Gmail?
On pervious versions of Google+, you could click on the arrow icon next to your name at the top of the chat list and select Sign out of chat. There appears to be no way to do this on the more recent versions. (Although, the users that did not yet activate the new Hangouts feature for Gmail, they still can. But it seems likely that Google will roll out Hangouts to all Gmail accounts as the only option. When that happens, it's indeed no longer possible.