It's bad enough team comms go over Slack so much now, at least we have email fallback. What scares me is for the teams that use Slack for system alerting.
And I'm in that boat of depending on Slack for alerting... in fact my team was also waiting over the holidays to deploy more robust non-Slack-based alerting (in our defense the product is only a few months old and only now starting to scale to any real volume).
I used to work for a place that had a FY that ended in summer. We had a lot less problems with stuff being shoveled out the door at Thanksgiving and Christmas because nobody was trying to finish their year-end performance goals over the Holidays.
I think what I'm implying is that management creates this issue, but we are complicit.
The holidays are actually the perfect time for Slack to roll out a risky deployment, as it has to be their lowest usage time. So it would make sense if something was pushed out last week or the week before. And everything probably seemed fine.
And then this morning they suddenly realize this new feature does not perform under load. And to make matters worse, the new feature has been out long enough to make any sort of rollback very tricky, if not impossible. Which means they'd need engineers to desperately hack out, test and deploy a code fix.
If this is the scenario, I do not envy them at all.
It broke, which was a major problem, this meant that senior management were being phoned (ho), and relatively high middle managers were on site to deal with the fall out. Of course most suppliers were also closed so everything was harder to fix.
There's good reasons not to do changes when places are closed, or at least skeletoned, for 2 weeks.
It seems a bit presumptuous to assume that's at fault here, given their age.
At one of my old jobs, we had SMS via two physical/hardware devices in our data center. One had a Telstra SIM card and the other had an Optus SIM card. (They were plugged into the same machine, but we had plans to put a second one in another data center before I left).
If you really care about alerts, you should have physical hardware doing your SMS messages via two different point-of-presences.
Hopefully email won't be your backup. I've seen that done. Alerts get filtered and ignored, often by accident.
Of course 2020 saw an increase, but it was smeared over a week or a month rather than being a big jump in a single day after everyone's holidays.