This rhetorical question is used to show how much David respected Abner. Here "fallen" is a euphemism that means "died." It can be translated as a statement. Alternate translation: "It is certainly true that a great prince has died today in Israel!" (See: [[rc://en/ta/man/jit/figs-rquestion]] and [[rc://en/ta/man/jit/figs-euphemism]])