IRC, Skype, Hipchat, Slack, Bluejeans, Hangouts, Zoom, ... - it all seems pretty interchangeable to me. My employer switched chat and videoconf providers a couple of times, and it's not a big deal. Which is why I think that Slack is not worth $10b but I'm sure that Goldman-Sachs will ignore my opinion and get the valuation they want anyway for an IPO ;-).
I don't think that running your own IRC server is a solution for any company - your admin hours are probably better spent elsewhere. That doesn't mean that I _like_ being forced to one chat client where IRC gave me integration wherever, however I wanted - in the CLI, in a 24x80 terminal, inside Emacs, under any GUI, and so on. But times go on and sound business reasoning precludes rolling your own if there are so many relatively cheap solutions out there that just work.