Q: Why did all the music on my ipod classic get erased and how can I avoid that happening in the future?

Disconnecting too quickly was the most likely cause. Make sure that everything you want on your iPod is in your library and that you have a backup to that just in case. See Backup your iTunes for Windows library with SyncToy for a suggested method.

tt2

I have had this problem for years. I do a combination of making sure I have the most recent version of iTunes, restoring the iPod (without it being connected to my PC), closing and restarting iTunes, and restarting my PC. Eventually doing this over and over I can get iTunes to restore my iPod. It really *****.