I've been pondering the issue of retrieving Charlotte Smythe's journal, and it occurred to me that since presumably the traitors are reading the responses, we could use the journal to communicate with them via private message. Perhaps we might offer young Meg's fellow traitors a bargain of sorts: if the journal is returned to us promptly, Meg will be transferred to Azkaban but will remain alive. If not, or if they write in it again ... well, I'm sure Auror Lestrange could think of a suitable response.
Their response would be instructive, if nothing else. Give us some sense of what they're made of.