I don't think they would discontinue Google Talk right away.

In the presentation, they said you can 'upgrade' to Hangouts in Gmail, clicking on your profile picture. I wonder what happens with your XMPP/Jabber connection then. I don't want to try it until I find viable alternative.

I guess it is going to look like other discontinued products (Reader, old Gmail, classic e-mail editing in Gmail...) - they will support it for few more months until everyone implements their proprietary API (if they release such).

What would be the point for Google to continue supporting Talk indefinitely, when they are publicly announcing the drop of XMPP in favor of unified chat.