Just out of curiosity, by your logic, there is always a backup.

So should AC have one spare B737 in YHZ? Or two (because, what if something happens to the first one, such as an OAL container blowing in the wind coming into contact with the AC aircraft causing damage)? Maybe 3 incase that 2nd one gets struck by lightning. Or a 4th incase of a bird strike?
How many backup crew members should there be? Maybe two pilots instead of one in case one of the backup pilots falls ill?
How many backup IFS crew members should there be?
etc. etc. etc.

You want the ticket prices to go up to justify the added expenses, right? And then no one will book the flight and the route gets dropped. All good, right?

BTW, I love how London is one of the foggiest places in the universe. I would have never guessed.