I have three further questions on standby crews someone may be able to answer:
What level of standby - if any - would a legacy carrier have down the route with overnighting crews (obviously not applicable to the example here).
What level of standby is required at bases and would crew actually be physically present or be available to be called in? If crew are present how long can they remain before going out of hours? Would BA for example need a new standby 747 crew every few hours. Presumably you can't hang around from the first flight of the day to the last.
Could a captain cover for a FO?