It actually happened to me. I forgot, called member services the very next day, and they said that I could not bank my points. Luckily I had already used half my points for the year.
What member services also told me is that I could deposit the points towards RCI, and that I would have up to 2 years to book that. Low and behold, I was getting married in 2 years, and I used it towards my honeymoon. I deposited the points that were going to expire at the end of the year into RCI. The year after, I booked a nice studio in Canada. It was 1 week for 120 points, + $100 booking fee. I really lucked out.