If the borrowed points come out of the reservation they will remain in your account as borrowed points and must be used by the end of the use year. The issue is whether borrowed points will in fact be leftover if reservaitons are switched. If in the the current reservation you have both borrowed and current use year points and a wait list for a new reservation comes through for fewer points than the total you are already using, then they will use for the new reservation first the borroed points and then the current points, so you may end up with just excess current points unless the new reservation requires fewer than all the borrowed points in the existing reservation.