Comment 4 for bug 514426

How about:

leaving the double click action "as is". E.g. when it is configured to open a chat window, when double clicking on a contact, but the contact is offline, then the message window appears. This I would leave as is.

However, when right clicking on an offline contact, right now the chat is disabled. We could probably enable this one. Then maybe in the window head line, adding some text e.g. "WARNING: chat with offline contact"

And when a chat window is open with someone, and the other party goes offline, we could still allow sending chat messages to that contact, but when the contact goes offline/invisible, changing the window line also adding a warning "WARNING: contact went offline"

With regard to the history, I would leave everything as is, not mixing up message with chat history... (do we actually have a message history?)

That would mean: no extra configuration option. "dumb" users, (I at least assume they are able to read) "may" see and read the warning when chatting with an offline contact.