Ah, yes, IRC has netsplits. Slack, on the other hand, has "reconnecting...", which I encounter a dozen times a day on it.
I guess it's down to personal preference whether you prefer being able to talk with a partial group knowing that some people are absent, and not being able to communicate at all.
Reconnecting in slack then shows you the missed messages. What's the common case for making sure participants have access to all past messages in IRC? An external log, which doesn't really solve the netsplit problem, because it necessarily is part of the split?
I would much prefer clear indication that there is a problem communicating with others so I can fall back to an alternative method of communication.
I guess it's down to personal preference whether you prefer being able to talk with a partial group knowing that some people are absent, and not being able to communicate at all.