I have to do some surgery as well, Anthony. I noticed mid winte rthat three or four heads of my M. plumosa were looking rather off colour, and decided to wait for Spring. Now there is fresh growth on the other heads, but the ones that were sick are now terminal, so I had better get on and repot and cut back.
If worst come sthe the worst, then I know there are some healthy heads and it'll have to be a re-rooting job, but this just happens sometimes for reasons that I cant explain. M. plumosa is known to be prone to this sort of thing.