Seems to be some health scare, hopefully nothing too bad. While maybe 70% of each album is a bit knuckle-dragging, when you gather up the other 30%'s across so many albums you get a cracking show. Best concert I was ever at (1991).
On a musical/stage performance level he wouldnt exactly be irreplaceable, but given the whole 'family' vibe to the thing I couldnt see them going on without him.