I would suggest mounting the plant. Keep the keikis attached to the old growths, a source of energy for them. Mount so that the keikis are next to the mount - that is where you will get the new roots. (Or if you see new growths starting, that would be the part to put against the mount.) Mine is just staring to produce new growth (blooming on leafless canes), this is a very good time for getting it re-established. You will need to spray it every day, mounted plants dry out fast. But that is exactly what this species needs. That sphagnum in the pot likely kept it far too wet.
Taking the optimistic view that it will put out new growth (I really think that it will), next winter it will lose leaves, at that time keep it drier but not completely dry. (Looks dead but it isn't!) I think that your climate is similar to mine. These can tolerate winter nights down to frost if kept fairly dry.
Also be sure there are not spider mites. Thin-leaved Dendrobiums are very susceptible to spider mites in hot, low humidity seasons.
This species doesn't like hot weather. I seem to recall your summer temperatures can get quite high. I wasn't able to keep it alive in my growing area where it was 30-35C in the summer, and not lower at night. Coastal southern California can see periods with daytime temperatures like that, but it is almost always cooler at night.
Like most Dendrobiums it needs a lot of water when making new growths, and it shouldn't dry out when in growth. But they often lose their roots and leaves when it is too hot.
As Roberta mentioned, consider mounting it on a piece of wood with a thin layer of sphagnum between the wood and the plant. Attach the plant so the keikis with their roots are in contact with the sphagnum. Or pot it in a wide enough pot you can set it sideways, with a thin layer of sphagnum on top, and the keikis and their roots touching the sphagnum.
My observation has been most people who kill Dendrobiums let them get too dry when they are making new growth. After that the problems are spider mites, sunburn and the wrong temperatures.
__________________ May the bridges I've burned light my way.
Another thought if you mount it... place the mount horizontally. It will hold moisture just a little bit longer than if it is vertical, but still have the advantage of maximum air around the roots (relative to potting) You can even soak the mount for 10-30 minutes, so that it holds some more water.