You could always keep them separate, if you wanted to. This feature was totally invisible to people who left it turned off.
I personally want to have all my messaging in one place, which used to be possible. Now everything is fragmented, and I constantly have to remember how each person in my life prefers to communicate, open the right app, find their name, and then message them. It's incredibly frustrating to have a worse 2017 messaging experience than I did in 2007 with my BlackBerry.
> This might be a naive question, but will chat within Gmail still work? Is that chat provided by Talk or Hangouts?
Chat in Gmail is Hangouts.