If you deposit the points into RCI, they will be valid for RCI exchanges for two years. Generally, the expiration date is actually the last day of the month two years after deposit -- so if you deposited on August 18, 2013, the points would expire on August 31, 2015.
Obviously, if you don't use the points for an RCI exchange, they are gone. If you do an exchange, you will also pay DVC their $95 exchange fee.
There is one other option if you know you're not doing a trip this summer, and it is NOT one MS will recommend to you because it competes with DVC.
That option is to rent those points...or more accurately, rent a reservation using those points. The DVC Rent/Trade board is one place to rent. Others are TUG and Redweek.
Also, David's rental service (dvcbyrequest. com) is another option. David serves as a broker between owners with points they can't use and renters.
A lot of the feasibility for either RCI or renting depends on how many points you have. If you don't have enough to make a reservation, neither option may be possible. OTOH, you'll sometimes find folks who want to rent only a short stay, which might be a perfect match.