The Yellow leaves aren't part of it's dieing-down phase....they're part
of it's dieing phase. Unfortunatly, this phase only occurs once in the
plants lifecycle.

Immediate changes in cultural practices are required if the thing has
any chance. First of all, yank it out of whatever it's potted in, and
chuck it (the stuff). Get some nice coarse chunks of bark or whatever
you'd like (clay) and repot in that. Trim all dead roots at least one
inch beyond rot / living tissue border WITH A STERILIZED INSTRUMENT.
Water much much less frequently. While you're on that many dendrobs
like to be pushed, than have a dormancy phase, your main goal right now
is to rescue that plant and it's inevitably weakened root system.
Fertilize (very) weakly, weekly. Watering needs will need to tuned by
you, depending on latitude, growing environment, circulation, potting
medium, species, humidity, temp.

I would also suggest removing some of the plants "maintenance" tissues.
This would include much older pseudobulbs with no photosynthetic
capacity. If all leaves are yellow, try cutting many of them right
through the middle, right across the leaf. This will also help reduce
the plants overall needs. If some leaves are still green, make every
effort to make those lil' photosynthesizing suckers happy. Try to
preserve as much photosynthetic surface area as possible. The idea is
to create a plant with more photosynthetic ability, than is required by
the plant for maintenance. The surplus of photosynthates facilatates
growth.