I had a community of people I would talk to on XMPP, the introduction of gchat brought more a lot more users we could IM with, gchat broke off from XMPP and most of my friends abandoned XMPP to stay with the userbase on gchat. I stayed logged on to XMPP for a while, a couple people did, but most of our discussions had moved to gchat. How can I come to any conclusion other than that this was connected to gchat?

The person you replied to was talking about killing an existing social network by making it irrelevant. A community can definitely be alive while being irrelevant “globally and in terms of social media”. It dies when it loses relevance to its userbase.