However, Bandcamp does abide by the laws that require them to stop distributing music at the rights holders' request.
No music service, or any service, for that matter, will guarantee access to files without regard to laws. Some will try harder, some have tried harder and been beaten down.
The most infuriating thing is that bandcamp gaslights you on it. I eventually confirmed that yes, I had bought that song, after tracking down the receipt in my email provider or something (it was hidden from purchase history, bandcamp "I can't find my music" link didn't mention this, etc etc).
This isn't just an issue for playing music though - if you buy a bunch of stuff but don't download it right away you could loose it too. I bought the track I mentioned right after it was released, and the substitution happened within a day or two of that.
Like, I get it, if there was some legal issue (pirated work - and then they should issue refunds). But the fact that bandcamp tries to hide it just means that they know they have no moral grounds here.