Isn't that a risk all customers take when they wait on a promotion. If the business is bought out they might lose that opportunity. The longer you wait to cash it in, the greater risk you will lose it.
I wouldn't bash the new owners for not fullfilling someone else's promotion. I'd let them know, politely, that you are disappointed that they won't honor it and then move on. It may be that they will provide better service, more desirable ammenities, and such - and those few days you "lost" will be nothing compared to what you gained.