Well, the question is whether or not your contributions to the chat are removed for everyone, or just for you.
I mean, my guild girlfriend could still show my irl girlfriend the messages I sent her if they're still in her inbox.
If I hit "leave convo," my comments would still show up in everyone else's inbox, right? I imagine so, since that is how it normally works.

Not that it really matters, because I'd just like to organize my inbox a bit. But its something to think about.