Although, oddly, I do have one album which is no longer available for streaming in the web client, but remains intact in the Android app.

I haven't had this problem, unless artists can do something that looks identical to this on the face.

I had an artist take "Album 1", "Album 2", "Album 3", and "Album 4", which I purchased through a whole-discography purchase, and merge them into "Album 1-4". It turns out I was able to download the originals anyways.

I haven't had this happen with albums that I can verify are currently unavailable on bandcamp, but I have ran into an issue before where an Artist updated the album with more tracks and a "remaster" which means I couldn't get the originals anymore. Luckily I usually buy the CD and keep it in storage as a backup I can rip from.