It would be like Boeing or Airbus announcing all the safety features on their airliners were non functioning.
To add to the other replies: I'm not trusting them with keeping my code safe (everybody has copies on their own computers). I'm trusting them with facilitating my workflow, helping me collaborate, and also to keep my issues etc. safe.
So yes, this can have a relatively large impact in terms of not being able to work as efficiently for a day and potentially losing some issues, but nowhere near as disastrous as losing all my code.
If you want to move it, in most cases you can simply create a new bare repo on another remote and push yours to it. It's probably the easiest system out there to simply pick up your data and go, unlike the walled gardens of social networking, video (YouTube isn't video, it's video + annotations + another ecosystem of tools that's not easy to export), and other services.
Even blog software isn't as resilient. You still have to export your Wordpress or Ghost blog when you want to move it. With git, when you work on it, you already have a full copy (with a few exceptions of course, like remote branches people prune without merging or local branches people never push).
This might be a good time to note that GitHub dropped their database awhile back (twice!). Bad Things always happen; you recover, learn, and hopefully fewer Bad Things happen in the future. Nature of the beast, unfortunately.
It can be argued that once a company messes up this bad it will make sure nothing similar happens ever again. However, it can also be argued that if a tech company has all five of its back up procedures fail it's borderline criminally negligent.
I have another company that runs on a completely open stack, where pretty much nothing is integrated by a specific vendor. We have hiccups, but we've never had the OS get hijacked and upgraded.
I've noticed most start-ups run by devs run on a more open stack and hack their way through problems on the cheap, and the ones run by corporate executives try to keep things as closed as possible, but end up spending millions to solve problems that they could have had some people solve for fun on the internet.
I prefer to use the right tool for the right job, but I wish companies like Microsoft would be more open when they cause huge issues that end up causing monetary loss. I make sure all my critical infrastructure is open source these days.
Weird that you group OSX in there. The only company in mainstream tech more secretive than Microsoft when it comes to problems is... Apple.
"Test-recover backups" is ops 101. "Monitor your backup process to be sure your backup store isn't empty" is ops 101. "Script your rollouts so you don't have an ops person doing SSH on boxes" is... ok, that one might be ops 102.
This points to a company with almost no understanding of how to operationalize software. There are certain to be far more landmines, possibly even bigger ones. Hiring an ops person to fix these problems is definitely possible - and I sincerely wish GitLab luck getting a competent ops team in place before the next crisis.