Den Spectabile seems to be dying

[estación seca]

I don't think it's fungus. I think you aren't watering enough. I think this has been the problem all along. In the breeze large bark dries quickly. This plant needs a lot of water.

I still see good roots. Don't cut anything off. Water every day. If you have time, water twice a day for a week or so.

The older part won't plump up, but new growth should be OK if it's going to survive.

[Jmarvin]

I will start daily watering today. Fingers crossed......

[Ben_in_North_FLA]

The dendrobium basics are as follows, grow in a bright light, use smaller pot as they have short rhyzome tween bulbs, stake and clip plant so there is NO movement when repotted, wait for new roots to resume normal watering, until then keep water to a minimum. Keep repotting to a minimum as dendrobiums do not like their roots disturbed and can take a long time to recover and in some cases do not recover... see your plant...., if not sure whether time to repot, wait another year, use lasting media (lava rocks/aliflor/coarse perlite with charcoal) if possible, let plant dry tween watering. Sometimes the truth can be a bit harsh but that is where culture is learned. I have made all these culture mishaps and also learned the hard way.
Clearly your last picture says it is time to ship this plant to the big greenhouse in the sky and start over, Climate wise SW Fla is conducive to grow dendrobiums like weeds. Spectabile should be fairly easy to find and replace. My suggestion is to get one that is from a local nursery (if possible) and potted in a pot/media where you do not have to disturb it by repotting. When the plant out grows the container, than you can move plant/roots/media to a bit larger container and just add more media without disturbing roots.
Best of luck....