Unless you have data in the service in some proprietary format, say.

If I had data locked up in some software I would rather have an ongoing relationship rather than just hope that they decide to make a new version when an OS update or other critical need arises.

"Data locked up in some software" in practice means strictly SaaS with cloud storage.

If you have the data locally, you can always migrate it - whether manually, through the software that made it (e.g. if the app isn't supporting your new OS, then run it in a VM with an older OS to export to a more forward-compatible format), or through third-party converters. If enough people are in this position, someone will write a solution.

If your data resides in the cloud, however, it's up to the vendor whether or not you'll be able to access it or export it, and how much of it. If they're just sunsetting the product, you probably, maybe, will be able to get some data back (which is almost definitely in some unknown ad-hoc format, quite likely a database dump in form of JSON, so you'll need a converter anyway). If they terminate your account because of $random reason, you won't even have a chance.

Or, to borrow a cliché, "not your files, not your data".

> or through third-party converters.

Assuming those exist.

They tend to for any software with non-negligible user base. The more so if those users suddenly all need one. Worst case, you can make one yourself. But none of that is even a possibility if the data is locked away in someone else's cloud.

These days its incredibly easy to find or write something up to extract data from a service. Take Spotify or Apple Music for example - its very easy to export out of either despite neither of it allowing it in their TOS or providing any tools to do so.

I suppose that's easy to get the contents of private Facebook groups, then?

Notice, getting stuff out of Facebook - or Twitter or similar walled-gardens - is double quandary. How you do scan/scrape/whatever the data and how do you avoid being banned for doing so. This given the formats/apis etc constantly and the degree of abusive platform protection also changing (we've seen Twitter's upheavals, imagine a similar abusive dictator buying Facebook and see how much he can squeeze).

And I'm sure someone will "you shoulda know about Facebook but my subscription sure ain't gonna trap me, no". Okay then...