The good news is that there's precedent for this. The image above, from a 2014 article by Steve Roach in Coin World, shows two Ambrotypes from the wreck of the SS "Central America," a side-wheel steamer that sank in 1857 off the Carolina coast. Although mostly known for its treasures of gold and silver, the wreck has also yielded many touching reminders of the human loss that attending its sinking, these images most poignant among them. Various articles on the wreck mention the recovery of both Daguerreotypes and Ambrotypes, although I've been unable to locate any images of the former. By 1857, the Daguerreotype would have been "old" technology, and probably far less common -- finding one in an 1857 wreck would be like finding an original iPhone in a car crash today -- unlikely, but certainly not impossible.
The survival status of such an image would also be very dependent on the technology. Ambrotypes are glass plates, with the image on the interior side of the glass, backed with black paper (the image is negative but appears positive -- in the UK they're sometimes referred to a "collodion positives." Since the collodion emulsion is inside the keep-case, such an image would be somewhat protected from water damage, and that's what we see in the image above; even though the decorative paper of the case has eroded away, the images seem intact.
For a Daguerreotype, though, the odds of survival might well be steeper. They consist of a sensitized copper plate which has been coated with silver and polished to a mirror-like sheen; the silver is sensitized and developed with vapors, and resides on an extraordinarily thin layer atop the silver. If you see an original, it still looks like a mirror when viewed straight-on; the image only appears at an angle. As surviving examples show, it's a fragile format; thoughtless attempts to "clean" a Daguerreotype with a cloth have led to irreparable damage.
In commercial use, Daguerreotypes were placed in a keep-case with a securely fastened glass plate as a cover -- but would Franklin's men have followed this procedure? The officer most closely associated with the apparatus was Goodsir, who as Assistant Surgeon and naturalist might also have found mollusks more interesting than men -- I'm not sure that dramatic finds such as those in Andrée's camera are likely. Still, one can always dream ...