If you haven't called MR to get a certificate issued at 7 days out, MR will automatically deduct the points and issue the certificate. If you don't have the points, the system will cancel your reservation. So basically, 1 week before (or earlier) if you know you're not going to have enough points you should call MR to convert the reservation or buy points. If you do convert to a cash reservation, it will be whatever the going rate is at the time (so could be high if the property is nearly sold out).

--Jon

P.S. My experience is with domestic US reservations. Since yours is overseas, you should check the reservation on the MR web site and verify it is still 7 days for auto booking of the certificate. It might be more than 7 days for your reservation....