What should happen if the SD card with the downloaded music on it is removed from the phone?
Pretty much any answer would be better than what actually happens today:
Spotify immediately switches back to using internal storage, and starts downloading all the music again, without even asking.
It does this even though there's nowhere near enough free space there for all the music. The only way I knew how to keep it from filling it up 100%, and probably crashing the whole phone, was to force-stop the Spotify app.
Putting the same SD card back in does nothing, since the app already reconfigured itself to use Internal storage. So, what happens when I set it back to external SD? It goes and *deletes* all the downloaded music, and starts downloading it again.
This is so completely absurd it would be funny if it happened to someone else! Unfortunately, with my phone (and I assume many others nowadays), the SD card and SIM card are in the same mounting bracket. So the SD card has to be removed to switch SIM cards.
This bit me really hard, as I deliberately downloaded a lot of music before going on an international trip. I even had to pay my ISP (Comcast, not recommended) an extra $10 for the privelege, since it put my over my 1TB/mo max data transfer. I figured it'd be worth it to have all my music with me while traveling. Of course, silly me forgot that the Spotify app is braindead. As soon as I arrived at the destination airport, I bought a local SIM card and went to put it in my phone... only to lose all all those downloads.