It would be complete chaos and close to what is happening in Greece today. There was widespread fear and shock after 9-11 for quite some time.Miss Texas our system of government is designed to function even if our president is killed.Kennedy proved that.admittedly the world is far more complex today.your point is well taken.overseas markets would be shaken at the least.we are all more connected today than ever before.
BTW - you do remember President Bush being whisked away first to Texas ( on 9-11 ) then to Kansas and then he told secret service " I want to go home" meaning the White House, don't you? This was only several hours after the bombing, so he cannot be considered a coward by any stretch of the imagination.
Those were horrible days and we don't want to ever forget it.