Symbolism, Imagery, Allegory
Henry V himself is a symbol of so many things in the play: England, kingship itself, the courage and macho necessary to dominate on the battlefield, the political savvy and sometimes ruthlessness needed to be a king, the generally-trying-to-be-a-good-guy qualities that balance out that ruthlessness—basically, if it has to do with awesome kingly leadership, Henry V represents it.
Because he represents so much awesome, Henry V's death makes us wonder if there's anyone who can fill his suit of armor. And as this play ends, the answer seems to be a pretty solid no. Henry VI might finally be old enough to rule, but he clearly lacks the savvy his father possessed—just consider his decision to ditch his fiancée for Margaret to see how naïve the young king is in action. Henry V's death is a constant reminder of just how uncertain England's future actually is; the leadership hole he left remains to be filled as the play ends.