One of the definitions of Demise is the end or failure of something (like a business, industry or system) or the death of someone that was considered to be powerful. So, a synonym for demise is "destruction," "death" or "passing". And since the excerpt is telling how the Ledstone's grandfather, who was a notorious bootlegger that killed many people, ended up being killed in a shoot-out, the sensational "demise" refers to the sensational "passing" of Ledstone's grandfather.
