From what the email I received from Google says, chatting over XMPP using a client like Pidgin or Adium should continue to work after the GTalk stuff is shut down in Gmail:
Third-party XMPP clients will continue to work with Hangouts for 1-on-1 chats after June 26. XMPP federation with third-party services providers will no longer be supported on June 26.
The talk about federation is referring to using Google Apps on your own domain. They dropped federation years ago for gmail.com, but I never knew they had kept it for private domains.
Keeping XMPP support at least is fortunate because Hangouts still lacks basic features like buddy lists. No, I don't want my entire list of contacts to me my buddies for hangouts. And yes I do want to see who's actually logged in at the time. Seems like Google isn't really sure what hangouts is. Is it just glorified SMS messaging (IE not necessarily interactive), is it Google voice? Is it Google Chat?
Sadly, Google doesn't seem to care that much about end users. Though I guess it's not surprising since we really are the product, not the customer. Google has done some amazing things that provide incredible conveniences to us, but I'm getting really tired of all the ADD hipsters that seem to have taken over on their development teams. It's getting rather fatiguing to have Google screwing up all the services I actually used (Picasa, GTalk, Google Voice).