I'm no genius w.r.t. petiolaris plants, having successfully killed
my falconeri from last year, but here's basic advice: Don't mess with
your mother stock. If you have just one plant, nurse it to health.
Sure, if any pieces break off accidentally---plant them up, but
otherwise let the plant go its own course. I don't know if a plant
regressing back into dormancy extracts some valuable chemical reserves
from its dying leaves, but it might. Once you have a sturdy, healthy
plant, then start propagating. This advice is of course modified if you
KNOW the mother plant is going to die for some reason