In a side note that someone else already made: it is interesting to see that many companies that uses JIRA also uses Slack but the noise/complaint/mentions comparing when Slack is down is way different. I barely saw people complaning.
I dunno about everyone else, but I'm generally frustrated and feel blocked when Slack is down, and I celebrate Jira being down because I've never had a pleasant experience using it. Jira is bureaucracy that gets in the way of me getting things done, and Slack is a critical communication path.
It's it though? You can hop onto any of a constellation of other IM platforms, FOSS and not fairly quickly for an instant comms channel, even if you're missing the history. Having all your issue tickets missing is something you can't really deal with unless you have a very recent dump, and even then you can't just fire up Bugzilla and get something working without a lot of migration and administrative effort.
You can do without JIRA for a week or two as long as managers understand and you all have a good concept of what work needed doing anyway. Then it starts getting dicey unless someone becomes a human JIRA to connect temporary manual bug tracking systems with everyone involved.
We have all sorts of slack channels set up to coordinate activity, so that internal customers can talk to engineers easily, or engineers can engage with each other. If slack goes down, we'd have to work all that out. For many days, it would be a huge drag on the process, slowing down interactions.
Other IM platforms wouldn't solve that just by existing. Sure, in principle one could set up such channels elsewhere, but that takes time, and the communication about it takes considerably more time.
Sounds like having a fallback pre-defined would be prudent if it's that important and you don't feel you could collectively extemporise something. "If Slack goes down, the plan is to use WhatsApp/Teams/Jeff's Matrix homeserver in his garage until service comes back. A list of group channels will be emailed if that happens."
Then if it does go down, you don't have to waste the first day arguing about the plan.
