The article doesn't really explain what happened to ICQ. It seems it was replaced by social networks which made building the social graph way simpler (you could find your friends by their names) and had messaging functionality. And once you have more friends there why use anything else?

Then came mobile-native messengers like WhatsApp and Telegram. Of course, ICQ also was native. I was running Jimm on my Nokia 6600. But it wasn't built for mobile as a product, wasn't focused on that.

By the way, has anything seen a good article on the demise of XMPP/Jabber/Gtalk?