Vets do not even know what the connection is between Cushing's disease and SARDS (Sudden Acquired Retinal Degeration Syndrome), but the two are connected somehow.
Unfortunately, a dog with SARDS will not regain its sight. When you get the test results back on Tuesday, if your dog is positive for Cushing's disease, the main thing you should keep in mind is that dogs who receive treatment for Cushing's disease do not live any longer than dogs who don't receive treatment. The medications do, however, make the symptoms a lot easier for the dog to live with, so while the length of his life won't be improved, his quality of life will be improved quite a bit.
Ghilly
I really don't know and can't be much help to you, as I have no experience with a Cushings dog.
I am sorry about your dog's illness, and hope that the vet will be able to help with supportive treatments.
It is of course very sad that she has suddenly lost her sight, and she will need a lot of understanding and support from you. But I have also heard that many dogs cope better than humans with sight loss, as their highly predominant sense of smell comes to the rescue.
If you can, do not re-arrange the furniture in your rooms. Keep things exactly the same for her. She will probably learn to cope, but she will need understanding and help until she gets used to this.
Try also, if you can, to keep 'upbeat' with her as much as possible. She wouldn't want to feel anything had gone wrong. They take their cue from our moods to a great extent.
I wish I could be of more help re: the prognosis of her blindness. I hope others will contribute to your thread, with their experiences.