Are Scroll Bars Dead?

I recently heard a designer say something to the effect that modern web designs don't use visual scrollbars - or at least they're only visible when scrolling. I'm a front-end developer and hadn't really heard this. Is there any truth to this? Specifically my question is:

For a web app, when content is scrollable:

  1. Should there ever be visible scroll bars (and why)?
  2. Should there ever not be visible scroll bars (and why not)?