I used to work for a relatively small dev-shop (9 persons) and we had two independent internet connections from two providers to avoid such problems. This was because done that way because there was only one fiber provider that wasn't really reliable (3+ hours downtimes every 1-2 months) and mobile tethering wasn't really an option as well because of nearby powerlines that made the reception quite a problem - to the point where our sales guy had to go outside the building during some calls. Luckily there was a second ISP - not really fast (10mbps was the best they could do) and quite expensive (we've paid more than twice more for that 10mbps than for a gigabit fiber), but still cheaper than having 9 people not able to work while waiting for the "main" ISP to solve their problems.

When this happens I just switch to tethering from my cell phone. Redundant enough.

So when Slack is down, just text your coworkers. Problem solved.

> f my local AT&T connection went down, it doesn't matter how open and resilient the Internet is, I'm not getting online until it's fixed.

Except that you could work from home, check your e-mail using mobile.