Comment 8 for bug 1779584

FWIW I'd prefer greying out missing tracks. Even though I don't know how this would be done it feels like that would be the simplest solution.
Because keeping the track references and playlist positions to allow restoring the previous playlist state requires something like keeping a complicated record of playlist changes to resolve situations where multiple tracks were removed (maybe at different points in time).

Another improvement for the library rescan would be a summary, like

  Library rescan finished.
  * 235 new tracks were found
  * 41 tracks have been moved
  * 12 tracks are missing