There are plenty of people who live betwee Sha Tin and Sheung Shui and works in Kowloon or HK Island. Why can't someone imagine a few hundred would still be enroute home before midnight on the East Rail, when that was the only transportation running?

That's EXACTLY the reason why MTR was running all service all night. They were basically THE transportation a good number of HK workers can rely on. Otherwise, they would have stopped running before the lines got cut.