Completely understand that, and it does seem that when watching from a channels client device, the streams always stop when the client disconnects, but as of now, I've had to stop using the streams in emby as I wake up to a full 480gb transcode ssd too often, smart errors abound!
In the end I would love to see emby fix this, as the dream is everything all in one place, but a manual stop would be a nice bandaid! Or of there is an api function of some sort, I could whip something up to stop the streams without a button, but from what I could glean, the channels api seems to be for client devices only.