I have always received my points back if I cancelled a point reservation prior to the cancellation deadline. I understand that if you cancel after the deadline, you will be charged for the room at a designated rate (not sure how they calculate it), rather than just charged the points for one night. This had never been an issue in the past because I never cancelled at the last minute. However, with the new cancellation policy, cancellations due to weather or travel delays will become very expensive. Why doesn't Marriott just charge one nights worth of MR points rather than charge for the unused room? This is especially problematic because it is very difficult to determine what that 'rate' will be. One night cancellation charge can consume my total budget planned for the trip.
I've looked into this for you and here's what I've found:
If you cancel within the allowed time-frame, you'll receive your points back. If you cancel outside of the allowed time-frame, you'll still receive points back, but will be charged one night's room and tax at the hotel's rack rate as a cancellation fee.
Hope this helps!