There are a few options that they adopt depending on the route and length of delay. If they delay is not too long they just fly at the later time. With the relatively gererous turn around times it doesn't take them long to catch up with the delay (a day or 2 at most).
If the flight has to be cancelled then they re-route. Their first choice is to use Star Alliance members (for ORD
they fly passengers MAN
and then on to ORD
For the Caribbean it's more complicated and I guess they just rebook on VS
, although that one's a guess.
Bear in mond they had the same problem with the BOM
flights (it was daily operated by 1 A330). If that went tech they rebooked on LH
It costs them a lot of money to rebook outside their Alliance, unless they have an agreement with another airline to take the tickets at face value (e.g. on the LHR
route there is an agreement that BA
can put their PAX on each other airlines if there is a cancellation and the face value will apply).