Just another reason for OSS projects to never trust closed (centralized!) protocols: no recourse when it (inevitably) hits the fan.
While this might be true, we are still trading more problems for fewer problems. Yes, we can't fix slack when it breaks, but it still breaks a lot less than when we were running our own internal chat client.
http://www.npr.org/sections/money/2015/07/29/427467598/episo...
Even if IRC isn't for you, there's XMPP, Mattermost [0], Let's Chat [1], and Zulip [2].
[0]: http://www.mattermost.org/
Just to add, you can use IRC clients to connect to Mattermost https://twitter.com/mattermosthq/status/668898122630721538