(Note to OP: Ferry service shuts down when typhoon signal 8 (T8 for short) or black rain warning is issued.)
With typhoons, the Hong Kong Observatory usually give advance warning on their website of an impending T8, and also on radio and tv, so the chance of being caught unaware and being stuck on HK Island or Kowloon is rare nowadays. Still, I guess that is a hassle if you want to get home at a certain time, as it of course disrupts your schedule.
However, with black rain warning, that could be a bit more tricky. Such warnings is harder to give in advance because its much harder to predict the exact threshold of rainfall amount that would trigger a back rainstorm warning. Usually the best the HKO can do is forecast heavy rains, which may or may not warrant a warning, depending on the amount. Often the back rain warning is issued suddenly, so you'll be stuck where you are when the warning is on. Although unlike T8, black rain warning usually (but not always) is shorter, so the disruption duration is normally less than T8.