From "The Rules" (page 7) --
On or before December 31 of the current year, Members may deposit any remaining “rescued” ClubPoints into RCI for future weekly and nightly exchange reservations. Rescued Points deposited into RCI are valid from the date of deposit through an additional calendar year. A Rescue Fee applies.
The Rules have answers these sorts of questions: http://www.hgvclubprogram.com/content/1Rules-ENG-Rev050615.pdf
BTW, in the current year, you can also book a future-year's RCI stay and the system with draw on your rescued points without charging you for a deposit. But if you cancel next year, you'd then have to deposit them to RCI to avoid a forfeit.