all airlines that we know have contingency plans in case of aircraft going U/S.
Eg. An airlines used to work for had contracts at right prices, in place in case of such thing happening.
eg.
1) contact airline A
2) contact airline B
etc.
For example, Nauru Airlines have an old NZ 733, sitting at BNE most/all of week.
So FJ could move one or more of their 738's or 737-700 onto NAN/SYD/NAN instead of A330-200 & they could bring in Nauru Airlines 733 to replace 738 or 737-700.
What would you rather, be delayed a lot of hours or be put on an older aircraft ?