The takeaway I'm getting from this story, and Mattermost, is:
1. Export your critical data from SaaS services if you're business cannot exists without them.
2. Test that this works before putting years of data into a service.
There's nothing wrong with SaaS services, they just mean users must do their due diligence in any business partnership. I can't see how a game company can put their resources into delivering this as an open source project with no future plans for monetization. Frankly, without monetization, open source projects generally wither up and disappear. Then you're no further ahead.
You know, my thinking on this has really changed. Consider how many relatively successful life-forms cannot exist without a very specific other species of life. It is also a good strategy to be flexible with your dependencies - but I think nature proves it's not required to survive and thrive.
Taking the long view, it's interesting to consider the possibility (which I'm sure has already happened multiple times in tech and elsewhere) when a company has absorbed it's dependency, and also when a dependency absorbs what was, at first, it's host, and successfully so.
The one thing that throws a monkey wrench into all of this is centralized human control, and a single mind is notoriously ephemeral, changing, and emotional. The CEO of your dependency might wake up one day from a terrible dream of humiliation and failure, and decide that he can't and won't just exist to serve his wretched, ungrateful customers in some insignificant and petty way, and will instead take a completely different path! (This risk is why greedy sociopaths make excellent corporate leaders: their drives are stable, predictable and unemotional, which makes them both competent and, ironically, safe.)
Let's ignore how "many relatively successful [extant] life-forms" versus the ones that had "evolutionary challenges." There is an enormous difference between a species survival depending on the existence of a prey species and a species survival depending upon the existence of another species for uninterrupted, cooperative and coordinated behavior. Your relation to your SaaS provider is not similar to the blue whale's relationship with krill, it is more like the goby and the shrimp.