No Google did not "kill off" XMPP. It's still out there and anyone can use it - https://xmpp.org/.
What happened is that instant messaging protocols became irrelevant for most people because of iMessage and other services. Google Talk itself ended up dying quite quickly and never reached popular mass. Google couldn't kill XMPP with a product no one really used.
Learning the wrong lessons just means repeating the same mistakes.
