I also do not think this was published as we see it. If you squint at the full image, the composition weakens. Squinting makes the box vanish. The box is currently transparent, an afterthought, drawn to improve depth or give weight to the cloaked man. It may have also improved the narrative? It may be were the rabbit came from, or were it will go? The bit at the top right may part of anther image or another afterthought that something needs to be added there? Possibly a page from a sketchbook and begs to be removed from the frame. If it were mine, I'd want to see if there is anything on beyond the mat or on the back of the page. It may also reveal what that partial writing says, if the page has been trimmed.
You have said what I know I need to do but don’t want to as the chances of me getting it back together as beautifully aren’t high! Maybe I will trot it into the framer in town and get him to do it, then I can get him to put it back together!
No actual answers from our corner, just our two cents' worth of general impressions... Really nice pen-&-ink-or-inkwash drawing... clearly a study, though, what with the "transparent" box at lower left, and the doodle (part of a face -- with a bloody nose, or an obscene amount of nostril hair? or just the bottom edge of a window curtain?) at the upper right... Knee-jerk reaction here was that the male figure was some sort of Puritan-era witchfinder or somesuch paid accuser... then, with the hare in his pocket, that he himself was a witch or warlock (rabbits and hares were often alleged to be witches' familiars), or maybe just a "stage magician" ("Watch me pull a rabbit outta this hat!")... Can't guess what the woman's rope is connected to, if anything -- maybe she's performing "the Hindoo Rope Trick"... Word or name at lower left -- "Siddon"? "Gliddon"? A misspelling of "widow" with two d's?
Yes,in a manner of speaking-THAT would be the Keene to own ! That is unless Whistler had done an oil portrait of him.