Internet Relay Chat Didn't Fall Off a Cliff
netsplit.de has explained - in very simple terms - that IRC is a "chat protocol that was developed in 1988 and that's internationally used for text based communication over the Internet. On IRC you can directly chat with individual persons via private messages or you can enter chat rooms (usually called channels) about many different topics."
4 years ago Freenode pretty much collapsed (it is still rather dodgy), unable to recover. It's still online, but few people connect to it. This is a chart of networks people still connect to this year:
IRC is not "mainstream" - not in the sense that CNN or BillBC will ever mention it - but it is a communications hub that's very useful to a lot of people. As long as many people continue to use IRC the development of IRC clients (or client software) will carry on. IRC will turn 40 in less than 3 years from now. Months prior to that our IRC community turns 20. █