do as I do just stop using the card but dont cancel it until you go thru at least one statement w/o any charges this way you'll keep all the pts you earned from the charges made. if Im correct the Hilton card doesnt carry an annual fee, so you lose nothing by waiting for a statement to process w/o any charges.
also I agree with what was stated above that the pts you'll lose will probably be for those charges that are on a statement that hasn't closed as yet, and not any previous ones. I had the Hilton Visa for 2 months and then cancelled I kept the 10,000 pts plus the pts for the few charges I made(the CDWwasnt good for 3 countries I travel to and the pts to miles 50000pts for 10000 miles didnt justify me keeping the card EVEN w/o a fee)