I've pondered the issue as to whether anyone has the obligation to unsticky them, as it was a conscious decision on their part. I assume they both had cellphones that they could use to call for help. If so, simply remove the valuable paintings from the room and turn out the lights for the night. To be generous, I'd leave them both a bucket, a couple of bottled waters and perhaps a loaf of bread.

Sometimes you need to provide a lesson for others contemplating similar tactics.