What server do you run? I'm planning to re-cloud my music, I mean I divide my music to two parts: that I listen to casually, and that which I want to own by myself. Spotify is so cheap it tempts really well, but I've already lost a few of my music from it (for example I had a title in my playlist, but it's lost, and I can't even see what the title was). I tend to re-buy each month a CD or two, so I re-own my music.

Not the person you asked, but I am running mpd[1] ("musicpd" in some package repos), using its httpd output to serve on localhost, and use a normal reverse proxy with Nginx to expose it on my VPN with HTTPS. To manage playlists and stuff, I connect to mpd from my LAN using ncmpcpp[2].

Nowadays there's probably better alternatives though.

[1]: https://www.musicpd.org/

[2]: https://github.com/ncmpcpp/ncmpcpp

Spotify has an option to show songs in your playlists which have been removed. In the mobile app, Settings->Content and Display->Show unplayable songs.

Hope this helps!