Points, in general, don't expire. But free night certificates do expire. If you're using a free night cert and cancel, they'll put that back into your account. The expiration date, most likely, will still hold. I have read accounts of folks calling Marriott or Chase and getting the dates extended. There should be a reservations number on your card. If you call that, the person may help or forward you to a real person, even on the weekend.