Hi Joe. I'm no expert on this species either, but I have several Zygo plants which have propagated themselves from a large mother plant over the last few years and they are all doing quite well.
It had been covered in leaf spot from the greenhouse conditions when we brought it home. If given the right growing conditions they grow pretty quickly
so I wouldn't be too concerned about the chances of survival for this plant. Despite it's unfortuate issues, you can save it. The new growths look like they're coming on fairly quickly and they will flower for you again in no time.
Have you repotted it yet into a medium grade fir bark/rockwol/charcoal mix? How are the roots? They sould be firm and white. That moss stuff stays wet too long (breaks down too fast as Phantasm said) and Zygo's aren't keen on that. I would also watch your watering habits and don't overpot it. The roots prefer to be a little tight.
What kind of fungicide are you using? I have found Safer's Defender (sulphur base) to be effective but there are other fungicides available too. You also need repeat applications to bring the spore population to heal. It would be wise to take a look at other orchids/plants in the area to see if they're also displaying similar spotting, if so, treat them too. Also good air circulation in very important. Bright light, like what you describe should be fine. Removing the worst of the leaves would be acceptable, and the flower spike sounds like it's done for, the plant will abort the flowers if it's under too much stress. Still the plant does need a few of the mature leaves to support the emerging young shoots, so it would be wise to leave the less affected ones. The new growth that you show in your pictures aren't looking that bad and will continue to mature into healthy growths if given the proper care.
Good luck.
Ok, getting off the soap box now.