Hypothetically speaking, if Emailkid had arrived in Shanghai, found that UA had cancelled the original flight, and the resolution was a replacement flight that went over the 48 hours TWOV limit, I'm pretty confident that the Chinese would have allowed dispensation for the overtime without kicking up a fuss. Note that this is a different condition than having an original scheduled connection that is over the 48 hours. Back to hypothesis, with so many *A flights out of Shanghai TPAC, it's unlikely that UA couldn't have found an alternative that didn't bust the TWOV max. Except in peak travel seasons, when the flights might be there but available seats not.