I was able to use CA Backup / Restore Appdata to make a backup, or at least a partial one. The Plex metadata seems to have survived. After making the backup, I stopped the array, disable the cache disk and shut down. Then, I replaced the drive and started the server. I enabled the cache drive, started the array and formatted the disk. After that, I used CA Backup / Restore appdata to restore the backup it had made. I then tried to start the Plex service but it wouldn't or couldn't find the metadata. I then tried using Krusader only to realize it wouldn't launch. I ended up recreating docker.img and reinstalling the Krusader and Plex containers. Now, both apps are working and Plex seems to back to normal, all custom artwork and organization survived.