For an example of when capacitive touch wonts work but the laptop would, simply get your finger a little bit wet.
The scenario I'm imagining is opening your computer only to discover that had closed it in the middle of a youtube video or something the night before, and it just continues playing where it left off. A crime of the highest order in OS design, to be sure, but hardly a rare occurrence.
I was imagining someone wearing a glove, but you are right that a certain amount of water will start causing issues. I think it would be difficult to pool enough water on both the touch bar and the trackpad outside of a catastrophe.
I can’t get sound to continue emitting after closing the lid. I’m sure an app can be developed to make that happen, but it wouldn’t be something commonly used. The most likely candidate seems to me to be something like audio performance software, but a person in that situation wouldn’t be using the speakers as an out and would be used to quickly dealing with software/hardware quirks.
Researching this conversation has been fun. :)