Sorry to read of the demise of your living stone!

I have had two and have the terrible habit of overwatering so until I break the habit I won't try again. I did find out there is a fungus that can cause root rot called Rhizactonia Root and Stem Rot . Maybe keeping a close eye on the others and reading the info might help. If you have this situation, perhaps you should follow the suggestions
Rhizoctonia is a fungus found in most soils that can enter the plant both through the roots and in to the plant at soil level. Besides the obvious of not overwatering but all the leaves from the bottom up are wilted, it is suggested you remove the plant ( isolate?).
Further suggestions are, if it was in a pot, discard the soil and wash the pot with a 1 part bleach to 9 parts water solution. Further info says Fungicides can be used but makes no suggestions as to which and you certainly need to use caution there!