Google will be discontinuing the Google Talk product on June 25, 2017 and will automatically transition all existing Google Talk chats to Google Hangouts. This will be a mandatory change implemented by Google.
How will this affect you?
If in your chat window you get a message and option to switch to Hangouts, please go ahead.
Otherwise, if you’re not using a third-party instant messaging (IM) client or special notification options, it probably won’t affect you.
If you’re using a third-party IM client, it will no longer work. The XMPP messaging that allowed these clients to work was a function of Talk and is not included with Hangouts.
If you have desktop notifications for incoming chat messages set up with Google Talk, some of those options will no longer be available in Google Hangouts.