Forgive me if I'm missing something, but I fail to see why you would want to keep the channel open after you've parted it. I mean, for most (if not all scripts) that reference text/actions in a channel, you have to be part of the channel in order to see these.
In my opinion, keeping a channel window open that you're not in, simply takes up extra resources and screen space that could be used for a channel that you are in.
I'm not saying that there can't be a situation where you would want a channel open and not be active in that channel, but at the moment (and I've been thinking about this since I saw the original post) I can't think of such a situation.
If you can provide me with an example of a situation as indicated above, I'd love to see it, in order to give it consideration.