Do not hesitate to cut off the dead parts of a hoya and start an new plant with the pieces. I usually wait too long before deciding to do this but from now on I will re-root the plant immediately when I notice they do not appear to be thriving. I grow all types of hoyas but from the beginning have have difficulty with the stiff-leafed species. They seem to root easily and then for no known reason, turn yellow and begin rotting at the stem/leaf junction. At this point, it is usually too late to save, but as soon as one leaf takes this downward turn I must cut the healthy vines and tuck into new media and start over.
I did this with my prized Hoya sp. Lata Iskandar and I am very happy with the results. I waited until the last moment to accomplish this task but luck was on my side since I now how have a happy healthy tiny started plant. If feel it will be much healthier than the plant than the older version I moved from down south. Lata Iskandar never seemed to adapt to its new environment and I am hopeful this new plant will do just that! I am hoping to see the fuzzy yellow balls which make up the cute blooms in the near future!