You did return and recover treasure. The use of the canvas as a 'burial' shawl happened via a private note to me. I assume it was because the 'fake ghost' was actually a rock with a green continual flame spell underneath the corpse of a human propped up with a stick.... and I just reread
the post carefully -- Paws used the cloth that was covering the canvas. So the canvas wasn't destroyed.
Kaiakas can have taken it, but he would have had to roll it up, which will have done significant damage to the painting (it being an oil painting that was relatively new). There's no way to have transported it and not damaged it. So it's a damaged painting. #phew