I am aware thanks to PPRuNe as well that a lot of things are happening behind the scenes to make up for a delay and pax are unaware of them. Often these things don't work as much the airline (and pax) would like and the delay is well preserved.
However I have two comments here: the first relates to an editorial read on the "airline business" magazine back in 1993 - a good carrier is one that handles irregular situations effectively. How AI fared here?
Second were pax kept informed of the situation? Where the only announcements made "ladies and gentlemen we landed at LGW please wait" and 8 hours later "we are leaving for LHR"?
Finally would a provision or buses airside-airside (for emergencies) would have helped? I understand 10 buses are not productive to lay around but they could have ferried crew and pax from LHR to LGW as well?