The short answer is there is no answer. Technically its your burden. Reality, if that happens and you are up front early with skeds and the DO, and you are not doing something fairly dumb (ie j/s lax-ewr to fly ewr-cdg an hour later) it is generally understood as a "stuff happens" thing. Your ACP will probably get a report on it, but no "discipline". All bets are off if this is your 4th time missing a flight in the past month....