130 year old pink small leaf Christmas cactus, root rot.
Family treasure. Losing it. Down to one stem, please help. What should we do?
It isn't dead, it is just unhappy. First, understand that holiday cactus needs fast-draining soil. When was it last repotted? If it has been a few years, buy a container one size larger than this one (it likes a snug fit) and give it fresh potting mix. To make it drain fast, either mix potting soil 50:50 with cactus mix or add 1/3 coarse sand to potting mix by volume. Among other reasons, potting mixes deteriorate over time and plants get rootbound. Repot every 4 years or so. In wintertime, don't fertilize and let the soil dry out between waterings - not totally, completely dry but have no detectable moisture 2 inches into the soil. I use the "heft" test as a dry plant is much lighter than one that has just been watered. This takes some experience so double check by working your finger 2 " down into the soil. True of many houseplants, the lower light levels in winter lead the plant to cease active growth of new leaves. During this time fertilizer and too much water become problems. When dealing with an old plant like this, some gardeners prune misplaced or woody/unproductive top-growth and prune a few roots, especially if they can't be straightened during repotting. Bright, ambient light is best for the remainder of the winter and an east-facing window during the growing season. Do not put it next to cold windows or drafty areas. In your picture, I see many layers of leaves flopping over each other. Layers next to the pot may not receive enough light and may die. Start your rehab with repotting in a fast-draining mix. Prune any roots that are too long or look/feel mushy. Taking a cutting in spring is also an acceptable way to keep an old, sentimental plant growing - a "rebirth" if you will. When you prune roots or stems, you also rejuvenate by stimulating new growth. Here is a great article on caring for Christmas cactus including an old one like yours. https://wimastergardener.org/article/holiday-cactus/