I'm very interested to hear/see the details around how all of this is handled, as well. While I did go through one particular instance personally at LHR, I was connecting from BA to AA, so BA had to handle my accommodations, but AA did the flight rebooking. Both airlines were working very closely together at the LHR transfer desk, though, ensuring people made it on to planes to get where they were going regardless of the originally booked carrier (e.g. I was offered BA options for my continuation, not just AA).