This document from the Timeshare Council provides a detailed analysis of options available to timeshare owners who are unable to make their payments: http://timesharecouncil.net/selling/walk-away-from-a-timeshare/.
Bottom line: In good times and bad, timeshare owners who want “out” generally need to sell their timeshare for less than its original purchase price. As the article notes, selling a timeshare is tough, and you will be lucky if you sell it for half of what you bought it for. Perhaps you may want …