Indeed. I understand the frustrations, I was going to go down for opening day myself. However with a new attraction, especially one utilising new technology like this, there is always a chance of things going wrong last minute. It's happened to Dollywood so it's not a surprise it's happened to Merlin!
I wouldn't expect Thorpe to refund external hotel bookings, if they did it would be outstanding customer service.
Maybe in the future they'll go down the Taron route of not announcing an opening date until they know 100% when it will open!