Your major concern should be that you are relying on the other iPod for your content. Since the only way to get music onto an iPod Classic is through iTunes, then surely you still have that music in your iTunes library on your computer, don't you?
If not, what are you intending to do when that iPod fails - and I can assure you, it will, one day.
I recommend that you address this situation now, before it's too late.
If you still have the music in an iTunes Library, back it up. An iPod is not a backup for your computer; instead, the computer is the backup for the iPod. But in addition, you should back up the computer's hard drive as well since they too can fail. User tt2 has a lot of information about backing up: Backup your iTunes for Windows library with SyncToy
If you no longer have your iTunes Library, you should consider recovering the music from your iPod (and anything else) so that you can recreate the Library, ready for the time when you need to find a replacement for the Classic. However, Syncing content is from iTunes to the iPod, not the other way round. Once again, tt2 has a lot of help about this: Recover your iTunes library from your iPod or iOS device
The other alternative of course, is to re-build your Library from the original sources you used, such as CDs, downloading purchases again etc.
