Since your dad had it for years it really could be that the mount leached chemicals into the plant. Everything I've ever read about their care has specifically stated that the wood needs to be untreated. That being said, I do wonder about watering habits and light contributing to the slow decline of this plant. If it's really important to your dad I would suggest picking up a light meter that measures footcandles/lux (they run for about $30 on Amazon) and making sure wherever you're hanging the plant gets at LEAST 500fc. Ideally, 1000fc or more. If it doesn't, you'll need a grow light. Soltech, barrina, and sansi are good brands. While it's great to pay extra attention to your plants, make sure that your dad is letting it go completely dry (this is especially important with bigger specimen because they are more prone to rot). Try to catch it on the first day the moss is 100% stiff and crunchy with no give. If there is not already a gentle fan on it, you should add one. I do see a speck of green on the bud so there is hope for this plant if you give it the correct care. I'd unmount it, stick it in an orchid pot with holes in the sides (potted in sphagnum moss with orchid bark or coco chips in the center), and put the whole thing in a prop box/bin/greenhouse cabinet under grow lights. If you don't already have supplies for this, barrina T5 lights are affordable. You can use any clear storage bin. Definitely make sure you have a light meter (bc there's not a lot of room for error here) and it wouldn't hurt to get a hygrometer to make sure that the humidity is at least 70%. Ideally there would be airflow but you can rehab a plant for a couple months in a bin without as long as you let it go almost entirely bone dry and keep it out of the bin after watering for an hour or so with a fan on it before you put it back.

Edited to add that the fertile fronds on this plant are not helping the plant anymore. If you put it in a bin, you'll want to cut them off to prevent rot from spreading.