For all Google Talk lovers, there is a bad news.Today Google’s Product Manager for Google Voice and Hangouts, Mayur Kamat, has announced that Google Talk app for Windows will be deprecated on February 23, 2015. It doesn’t mean that Google Talk will not work anymore after February 23. It will still work but it will stop receiving updates and may break(stop working) any time in the future.
Kamat Says:

For some time now, our team has shared that we plan to focus our efforts on Hangouts. The Google Talk app for Windows will be deprecated on February 23, 2015. This will allow us to focus on bringing you the most robust and expressive communications experience with Google Hangouts.

However third party apps like Pidgin, Trillian etc and all other compatible apps will continue to work.
Kamat:

If you’re not ready to make the switch to Hangouts quite yet, you can continue using Google Talk on Windows with a range of compatible third-party chat apps (http://goo.gl/FSbCX5). Please keep in mind these aren’t Google products, so exercise caution when signing in with your Google account.

As there will no more updates to the Google Talk app and it may stop working anytime in future, so it might be the best time for you to move to Hangouts by using Gmail or chrome app. Google says that it is focusing on making Hangouts better. Lets see it can keep Google Talk users satisfied with Hangouts or not…

Source: Mayur Kamat