Well - have been on the phone with reservations for almost two hours and I am being told that they can not change the booking over to Westin, stating that this property is not available.
They stated, that they sent a message to the Westin if they could help/open up some rooms.
Overall, I find it very poor procedures to give customers 5 (five!) days notice of a partner to leave the program. Not sure, what is usually typical in this industry.

PS: I did see award availability last night, but figured I will call this morning, when reservation desks are staffed with folks, who have experience handling such issues.