If the artist is having a rough time of it, they can cancel and issue a refund. Dragging out a commission for so long and then ignoring a customer is unprofessional. Taking on new work and seeking out art trades when they owe past work (http://comments.deviantart.com/4/32868625/4366256032) is not a good way to conduct business.

One beware won't hurt the artist if they come in here, apologize, and make a good faith effort to resolve this situation.