oh my well
you can take a sharpy and mark where the rot lines are and watch day by day and if it grows i say you have to cut BUT you will loose the grafted part which means whatever it was to bloom as its not going to
OR you could try to cut away layer by layer and hop the rot is not more then 1/2 way threw and it might callous over and it might be able to be saves but that is not likely. I would have to see in person and see how far it has rotted threw . if you do cut you can peroxide it dry it and cinnamon keep that area very dry hope for the best..... i dont know what i would do with out putting my hands on it. if it where mine i would try to root the part from the top that is not rotted OR try to graft on a different rootstock.
