This has happened to me with iTunes, and Apple's contention in the suit has been expressed to me by Apple support.

A few months ago, I was browsing my iTunes cloud library and noticed that an album I had purchased years prior was missing a few songs. I contacted support, and the support agent explained to me that the rights holder had removed the songs from the store, and thus they were now removed from my library. (Inexplicably, the entire album is still available on iTunes, but apparently the version I bought was removed.)

The rep also helpfully recommended that I back up my downloads in the future. While I did in fact have all the songs downloaded on my Mac, I’m not sure what the official solution would be for someone whose primary device is an iPad or an iPhone.