Yes, I asked the agent to rebook me a direct flight in ROC, but she insisted that she needed to stick to the original itinerary... which I tried to argue but didn't succeed. Well... hope my father will get home just fine, he is still in LAX now.

If what the manager said was true, basically my conclusion is to try to avoid mixed carrier itinerary in the future. You will be stranded if anything happens, because neither side wants to take the responsibility. (AirChina keeps on telling my father that he should talk to United, err...)