FWIW, Google Groups powers email distribution lists for Gmail for Work. Or at least, the two are strongly linked.

At this point, unlike Reader, there's real cash behind the functionality. It's possible they could just fold it into Gmail, I guess, but with other mail interfaces like Inbox popping up in the Google ecosystem it seems if anything they're trying not to shoehorn too much more into a flagship product.

My guess is Groups will stick around for a while yet.