Without a good embalmer it wouldn't last 60 years, let alone 6,000 years. What ever external forces preserved it beyond its "shelf life" disrupted any decomposition processes so presumptions have no place in the discussion.
Perhaps hot water is a good embalmer. We find mammoth carcases with considerable skin intact often, in deep cuts in soft sandstone, near Antioch and Brentwood, and once in Blackhawk (Danville). Its always the same kind of formation. The skin will be like hard rawhide, crumbly, with sparse dark brown to almost black hair.