It is not known what "the fall of the eleventh" refers to exactly, but according to the prophecy, it must take place before the Question is asked. There is a candidate for the "fall of the eleventh," and that is the Doctor turning off the TARDIS' anti-gravs and literally falling on Trenzalore with Clara. This fits as it takes place before the Question is asked, and when Clara asks "How do we get down? Do we jump?", the Doctor explicitly corrects her by saying, "Don't be silly. We fall."
As for "silence will fall," that is not a part of the prophecy. That is the Silence's driving creed. In "The Wedding of River Song", the Doctor explained to Winston Churchill that the Silence want to kill him before he goes to Trenzalore so that he cannot answer the Question. If the Doctor is dead, then when the Question is asked, his "silence" will fall since he will be unable to answer. And since the Doctor is not, in fact, dead, his "silence" cannot fall.