Slack* and Discord do everything better than IRC does. Easier to use, more features, better usability, no computer jargon. Almost any IM software beats email in everything. Nowadays only technical people use FTP to transfer files online.
Services always seem die at some point. Think of the websites and software you used to communicate twenty years ago or ten years ago? ICQ was my first IM program and while it’s still technically alive, it’s not something anyone I know uses anymore. Microsoft’s Messenger is mostly dead. The early king of social media, MySpace, fell into irrelevancy and relaunched in 2012 as a music-social-media-something-something platform.
Protocols however, last from decade to decade. I’ve used IRC since 1998 and while there has been a significant dip popularity, it’s still going strong. As obsolete and confusing email can be (think “Re:Re:Re–” and nesting 10 mails deep), it’s still by far the biggest and most popular form of electronic communication in the business world.
Of course some services last longer than others. Right now it’s hard to see giants like Facebook Messenger or WhatsApp going away anytime soon. But once they do, I’ll still have a dusty RasperyPi running irssi in the corner.
Disclosure: I’ve never actually used Slack, just heard the hype.