I don't think Lucas ever mentioned JarJar's death, and never will. He simply faded away that character, as he did with Naboo. And how could Naboo be exploded by the prototype death star, if no one knew about it until ANH? Hmn... That brings a whole new question: how much did they know about the Death Star anyway? Leia had the plans hidden into the R2 unity, but they she know about the destructive power of it? Perhaps Bail Organa knew all along, and sent her to get those plans?