They need to be used by the end of the following use year -- the year you banked them into.
This will depend on when you cancel the trip, and whether the new trip falls within the same use year as the one you canceled.
Borrowed points will be returned to the use year in which the trip was scheduled. They cannot be returned to their original use year. When is the trip you're canceling, and when is the trip you want to re-book? Are they both within the same use year? If so, you can re-use your borrowed points for the next trip.
There are also some cancellation rules to consider. If you cancel a trip more than 30 days from check-in date, the points are returned to the use year in which the trip fell. You can use these points without restriction. If the points weren't previously banked or borrowed, and you are still within the banking deadline for your use year, you can also bank the points.
If you cancel 1-30 days before your check-in date, the points will be put in what's called a holding account. Points in holding have restrictions on how they can be used. Holding account points can't be banked.
If you cancel on your check-in date, or are a no-show without calling either Member Services or the resort front desk, all points associated with the reservation are forfeited.